Machine monsters are extremely powerful, and sometimes scary to face in battle. They rely on high ATK to beat the enemy down, while also using a variety of amazing techniques, ranging from piercing damage, card destruction, deck searching and much more. Machines are usually DARK, EARTH or LIGHT attributes and have some of the best support in the game.
History:
In the first season of Yu-Gi-Oh!, Machines were immune to Magic cards, as well as Spellcaster attacks, can you image how broken that would be today? Its a good thing they didn't make those effects real.
Machines have only have three structure decks so far, all of which have some decent cards in them. Machine Re-Volt gave us the powerful Ancient Gear Gadjiltron Dragon, while Machina Mayhem gave us the Machina Archetype as well as Machina Fortress. Cyber Dragon Revolution turned the old fan favourite Cyber Dragon into a deadly OTK deck.
Table of Contents:
Ancient Gears
Gadgets
Cyberdark
VWXYZ
Machina
Meklords
Karakuri
Geargia
Ally of Justice
Morphtronic
Mecha Phantom Beasts
Cyber
Qliphort
Ancient Gears:
Quick Overview:
Ancient Gears were introduced when they were used by Dr. Vellian Crowler in the Yu-Gi-Oh! GX series. They are EARTH attribute and have an amazing effect that prevents the opponent from activating Spell or Trap Cards when they attack. No more Mirror Force, Dimension Prison, etc.
They were released in The Lost Millennium and Shadow of Infinity booster packs, and then received their very own structure deck, Machine Re-Volt.
Spoiler:

Ancient Gear Gadjiltron Dragon
If this card attacks, your opponent cannot activate any Spell/Trap Cards until the end of the Damage Step. This card gets extra effects if you Tribute Summon it by Tributing ● Green Gadget: During battle between this attacking card and a Defense Position monster whose DEF is lower than the ATK of this card, inflict the difference as Battle Damage to your opponent. ● Red Gadget: When this card inflicts Battle Damage to your opponent, inflict 400 damage to your opponent. ● Yellow Gadget: If this card destroys your opponent's monster by battle, inflict 600 damage to your opponent.
This is the probably the best card of the deck. You should never tribute summon this guy, you always use Geartown for it. Being a level 8 also makes it a Trade-In target which is good.
Run 2-3

Ancient Gear Beast
This card cannot be Special Summoned. The effects of your opponent's monsters that this card destroys by battle are negated. If this card attacks, your opponent cannot activate any Spell or Trap Cards until the end of the Damage Step.
Really good card. Floaters won't get there effects off if this card attacks. You can normal summon this guy with Geartown out which is really good.
Run 1

Ancient Gear Knight
This card is treated as a Normal Monster while face-up on the field or in the Graveyard. While this card is face-up on the field, you can Normal Summon it to have it be treated as an Effect Monster with this effect:
● If this card attacks, your opponent cannot activate Spell or Trap Cards until the end of the Damage Step.
This is a really good card. Being a gemini is odd, but it's not bad either as it lets you run Gemini Spark.
Run 2-3

Ancient Gear Engineer
Negate the effect of any Trap Card that targets this card, and destroy that Trap Card. If this card attacks, your opponent cannot activate any Spell or Trap Cards until the end of the Damage Step. When this card attacks, destroy 1 Spell or Trap Card on your opponent's side of the field at the end of the Damage Step.
Probably one of the best Ancient Gear monsters. You can normal summon it with Geartown. This card is basically immune to traps, and picks apart your opponents backrow. It's just a shame that his stats aren't that great, and he is a level 5.
Run 1-2

Geartown
Both players can Tribute Summon "Ancient Gear" monsters with 1 less Tribute than required. When this card is destroyed and sent to the Graveyard, you can Special Summon 1 "Ancient Gear" monster from your hand, Deck, or Graveyard.
Fantastic card. Destroy and you get your Gadjiltron Dragon out, and it let's you summon all of your bigger monsters easier.
Run 3

Ancient Gear Castle
Face-up "Ancient Gear" monsters gain 300 ATK. Each time a monster(s) is Normal Summoned or Set, put 1 counter on this card. If you Tribute Summon an "Ancient Gear" monster, you can substitute this card for a Tribute(s), if the number of counters is equal to or greater than the number of required Tribute(s).
This is a cool card. It lets you summon your bigger monsters easier. I would only use this card if you're running Ancient Gear Golem. If you are;
Run 2-3

Ancient Gear Workshop
Add 1 "Ancient Gear" monster from your Graveyard to your hand.
Simple and good. Grab back a Gadjiltron and instantly dump it for Trade-In. Grab back a Knight and Gemini Spark it.
Run 2-3

Ancient Gear Drill
Activate only while you control a face-up "Ancient Gear" monster. Discard 1 card from your hand. Select 1 Spell Card from your Deck and Set it. You cannot use that Spell Card this turn.
Decent card. Grabs ANY spell card, not just Ancient Gear ones. I wouldn't really bother running it, but that doesn't mean the card is bad.
Run 1-2
Spoiler:

Ancient Gear Golem
This card cannot be Special Summoned. If this card attacks a Defense Position monster, inflict Piercing Battle Damage to your opponent. If this card attacks, your opponent cannot activate any Spell or Trap Cards until the end of the Damage Step.
This card is great. It's just a shame it can't be special summoned. Normally, don't run this card at all, but if you are going too;
Run 1-2

Ancient Gear Soldier
If this card attacks, your opponent cannot activate any Spell or Trap Cards until the end of the Damage Step.
Good effect, but bad stats. Ancient Gear Knight is better.
Run 0

Ancient Gear Cannon
By Tributing this card, inflict 500 damage to your opponent, and then neither player can activate Trap Cards during the Battle Phase of this turn.
Terrible effect. Why would you care if your opponent can't use trap cards? You're running Ancient Gears for crying out loud.
Run 0

Ancient Gear
While an "Ancient Gear" is face-up on your side of the field, you can Special Summon this card from your hand in Attack Position.
People like running this card with Machine Duplication, but I don't see the point. Cool, you just summoned 3 useless monsters to the field, now they have to sit there until next turn before you can tribute them for a monster.
Run 0

Ancient Gear Gadjiltron Chimera
If you Tribute Summon this card by Tributing 1 of the following monster(s), this card gets the appropriate effect: ● "Green Gadget": Increase this card's ATK by 300. ● "Red Gadget": When this card successfully attacks your opponent directly, inflict 500 points of damage to your opponent's Life Points. ● "Yellow Gadget": When this card destroys an opponent's monster in battle, inflict 700 points damage to your opponent's Life Points.
I really love this cards artwork, it's just a shame it's effects suck.
Run 0

Spell Gear
Send 3 face-up "Ancient Gear" cards you control to the Graveyard. You can Special Summon up to 1 "Ancient Gear Golem" from your hand and 1 from your Deck, ignoring the Summoning Conditions. Then, destroy all monsters you control except "Ancient Gear Golems". You cannot Normal Summon or Set until the end of your next turn.
Terrible card. Sure 2 Ancient Gear Golems are nice, but the that's a lot of cards just for that.
Run 0

Ancient Gear Fist
Equip only to an "Ancient Gear" monster. Destroy any monster that battles with it, at the end of the Damage Step.
Most archetypes have those bad equip cards. This is one of them.
Run 0

Ancient Gear Tank
Equip only to an "Ancient Gear" monster. It gains 600 ATK. When this card is destroyed and sent to the Graveyard, inflict 600 damage to your opponent.
A better Black Pendant. Still not that good.
Run 0

Ancient Gear Factory
Select 1 "Ancient Gear" monster in your hand and show it to your opponent. Remove from play "Ancient Gear" cards in your Graveyard whose total Levels are equal to double the selected card's. You can Normal Summon the selected card without Tributes this turn.
It's a very interesting card, I will give it that. You don't really run enough monsters to pull this off, and all your monsters levels are all over the place, so pulling this card off is hard.
Run 0
Spoiler:

Giant Rat
When this card is destroyed by battle and sent to the Graveyard: You can Special Summon 1 EARTH monster with 1500 or less ATK from your Deck, in face-up Attack Position.
Decent card. It's a floater that can grab Engineer. If you choose to run this card;
Run 1-2

Malefic Stardust Dragon
Cannot be Normal Summoned or Set. Must be Special Summoned (from your hand) by banishing 1 "Stardust Dragon" from your Extra Deck and cannot be Special Summoned by other ways. There can only be 1 face-up "Malefic" monster on the field. Face-up Field Spell Cards cannot be destroyed by effects. Other monsters you control cannot declare an attack. If there is no face-up Field Spell Card on the field, destroy this card.
You might be thinking why you should be running this card. It isn't for protecting Geartown, it's for the amazing rank 8 monsters this card can make. Geartown makes Gadjiltron super easily, so when you have Gadjiltron out, special summon this card, and overlay into something amazing like Divine Dragon Knight Felgrand. Malefic Stardust is also a Trade-In target.
Run 2-3

Trade-In
Discard 1 Level 8 monster; draw 2 cards.
Pretty self explanatory.
Run 2-3

Gemini Spark
Tribute 1 face-up Level 4 Gemini monster, then target 1 card on the field; destroy it, and if you do, draw 1 card.
Great card. Attack with Knight, bait out some backrow, then pop something else with this.
Run 2-3

Magical Hats
During your opponent's Battle Phase: Choose 2 non-Monster Cards from your Deck and 1 monster you control. Shuffle those 3 cards and Set them on the field in Defense Position. The 2 cards chosen from your Deck are treated as Normal Monsters (ATK 0/DEF 0) and are destroyed at the end of the Battle Phase.
Fantastic card for the deck. Activate this if they try running over Engineer and set Geartowns. You can get real creative with this card and run cards like Breakthrough Skill as well.
Run 1-2
Quick Overview:
Gadgets are a small archetype of EARTH Attribute Machines whose effects activate when summoned to add another Gadget of a differant colour to your hand. These cards are very splashable and work great with many other cards.
Spoiler:

Green Gadget
When you Normal Summon or Special Summon this card, you can add 1 "Red Gadget" from your Deck to your hand.

Red Gadget
When you Normal Summon or Special Summon this card, you can add 1 "Yellow Gadget" from your Deck to your hand.

Yellow Gadget
When you Normal Summon or Special Summon this card, you can add 1 "Green Gadget" from your Deck to your hand.
Not really much to talk about with the Gadgets, its pretty self explanatory, you summon one and it searches another.
Run 2-3 of each.
Make sure you run the same number of each card though.
Spoiler:

Tin Goldfish
When this card is Normal Summoned: You can Special Summon 1 Level 4 monster from your hand.
Fantastic card for the deck. It triggers all of the Gadgets search effects, as well as makes one turn Xyz monsters.
Run 3

Kagetokage
Cannot be Normal Summoned/Set. When you Normal Summon a Level 4 monster: You can Special Summon this card from your hand. This card cannot be used as a Synchro Material Monster.
Another great card for the deck. Summon a Gadget and then special summon this guy. If you're going to run this card, make sure you run King of the Feral Imps as well.
Run 2-3

Ultimate Offering
You can pay 500 Life Points to Normal Summon or Set 1 extra monster. You can only activate this effect during your Main Phase or your opponent's Battle Phase.
Even though this card is banned, i'm going to keep it here anyway. This card was stupid good with the Gadgets. Summon, search, summon, search, summon, search.
Quick Overview:
Cyberdarks are a small archetype of Machines that have the effect to be equip with Dragon monsters. They are very similar in that way to Dragunities. In Yu-Gi-Oh! GX, Zane started using Cyberdark's when he become an underground duelist.
Spoiler:

CyberDark Horn
When this card is Normal Summoned, select 1 Level 3 or lower Dragon-Type monster in your Graveyard and equip it to this card. This card gains ATK equal to the equipped card's ATK. During battle between this attacking card and a Defense Position monster whose DEF is lower than the ATK of this card, inflict the difference as Battle Damage to your opponent. If this card would be destroyed by battle, the equipped monster is destroyed instead.
Piercing damage is alright. You don't really have much of a choice of running though.
Run 2

CyberDark Edge
When this card is Normal Summoned, select 1 Level 3 or lower Dragon-Type monster in your Graveyard and equip it to this card. This card gains ATK equal to the equipped card's ATK. This card can attack your opponent directly. If it attacks using this effect, its ATK is halved during damage calculation only. If this card would be destroyed by battle, the equipped monster is destroyed instead.
Attacking directly is pretty neat, even if it is halved.
Run 2

CyberDark Keel
When this card is Normal Summoned, select 1 Level 3 or lower Dragon-Type monster in your Graveyard and equip it to this card. This card gains ATK equal to the equipped card's ATK. If this card destroys an opponent's monster by battle, inflict 300 damage to your opponent. If this card would be destroyed by battle, the equipped monster is destroyed instead.
I don't know why Konami bothers with such low amounts of effect damage.
Run 2

CyberDark Dragon
"Cyberdark Horn" + "Cyberdark Edge" + "Cyberdark Keel"
This monster cannot be Special Summoned except by Fusion Summon. When this monster is Special Summoned, select 1 Dragon-Type monster in your Graveyard and equip it to this card. This card gains ATK equal to the equipped card's ATK. This card gains 100 ATK for each Monster Card in your Graveyard. If this card would be destroyed by battle, the equipped monster is destroyed instead.
Great card. With the right equip monster, this card will became a massive beatstick.
Run 1-2

CyberDark Impact!
Return 1 "Cyberdark Edge", "Cyberdark Keel" and "Cyberdark Horn" from your side of the field, hand, or Graveyard to your Deck. Special Summon 1 "Cyberdark Dragon" from your Extra Deck. (This Special Summon is treated as a Fusion Summon.)
Fantastic card. This will be your main fusion summoning card. It's just a shame the card is so expensive in real life.
Run 2-3
Spoiler:

Black Salvo
When this card is Normal Summoned, you can select 1 Level 4 DARK Machine-Type monster from your Graveyard, and Special Summon it in face-up Defense Position. Its effect(s) is negated.
This card has great synergy with the deck. You can summon this card, grab back a Cyberdark, synchro into Black Rose Dragon and nuke the field, the proceed to Cyberdark Impact! and get a Cyberdark Dragon with a Black Rose Dragon as an equip.
Run 2-3

Delta Flyer
Once per turn, you can select 1 other face-up monster you control and increase its Level by 1.
Being 1500 attack, he is probably the best low level monster to have for you Cyberdark monsters. Also being tuner is great.
Run 1-2

Hunter Dragon
This dragon has taken down countless prey with its sharp fangs. It strikes very quickly, because if it does not strike first, it is vulnerable to a counter-attack.
Your strongest card to attached to your CyberDarks. Being a vanilla monster though, it's not recommended that you use it. Use it if you want though.
Run 0

Twin-Headed Behemoth
If this card is destroyed and sent from the field to the Graveyard, Special Summon it during the End Phase of this turn with 1000 ATK and 1000 DEF. Each player can only use the effect of "Twin-Headed Behemoth" once per Duel.
The good thing about Twin-Headed Behemoth is that its effect can activate while its attached to a Cyberdark Monster.
Run 0-1

Dragunity Aklys
When this card is Normal Summoned, you can Special Summon 1 "Dragunity" monster from your hand, then equip it with this card. When this card is sent to the Graveyard while equipped to a monster, select 1 card on the field, and destroy it.
Great card for your weaker Cyberdark monsters. Poping a card when it dies is fantastic.
Run 1-2

Dragunity Corsesca
This effect can only be activated while this card is equipped to a monster. If the equipped monster destroys an opponent's monster by battle, you can add 1 Level 4 or lower monster from your Deck to your hand with the same Type and Attribute as the monster this card is equipped to.
This effect is fantastic. Every time your Cyberdark monsters destroy a monster, you can grab another Cyberdark monster from your deck to your hand which will make your fusion summons easier.
Run 2

Dragunity Phalanx
Once per turn, while this card is equipped to a monster as an Equip Card by a card effect, you can Special Summon this card.
Another great card for your Cyberdark monsters. It makes level 6 synchros super easy.
Run 1
Quick Overview:
The "VWXYZ" Machines are all LIGHT Attribute monsters. They are not a archetype so have no support, so your going to have to be very creative if your using these cards. They do not need Polymerization, instead they combine with each other to form more power creations.
Spoiler:

V-Tiger Jet
This ace fighter is unbeatable in a dogfight. It combines with other monsters to launch an array of encircling attacks.

W-Wing Catapult
Once per turn, during your Main Phase, if you control this card on the field, you can equip it to your "V-Tiger Jet" as an Equip Card, OR unequip the Union equipment and Special Summon this card in face-up Attack Position. While equipped to a monster by this card's effect, increase the ATK and DEF of the equipped monster by 400 points. (1 monster can only be equipped with 1 Union Monster at a time. If the equipped monster is destroyed as a result of battle, destroy this card instead.)

X-Head Cannon
A monster with a mighty cannon barrel, it is able to integrate its attacks. It attacks in many ways by combining and separating with other monsters.

Y-Dragon Head
Once per turn, during your Main Phase, you can equip this card to "X-Head Cannon" you control as an Equip Card, OR unequip it to Special Summon this card in face-up Attack Position. While equipped to a monster by this effect, that monster gains 400 ATK and DEF. (A monster can only be equipped with 1 Union Monster at a time. If the equipped monster would be destroyed by battle, destroy this card instead.)

Z-Metal Tank
Once per turn, during your Main Phase, you can equip this card to "X-Head Cannon" or "Y-Dragon Head" you control as an Equip Card, OR unequip it to Special Summon this card in face-up Attack Position. While equipped to a monster by this effect, that monster gains 600 ATK and DEF. (A monster can only be equipped with 1 Union Monster at a time. If the equipped monster would be destroyed by battle, destroy this card instead.)
They are all pretty self explanatory. The effect monsters equip to there corresponding vanilla monster and boost that monsters attack.
Run 2 of each.
Spoiler:

XY-Dragon Cannon
"X-Head Cannon" + "Y-Dragon Head"
This card can only be Special Summoned from your Extra Deck by removing from play the above cards on your side of the field. (You do not use "Polymerization"). Discard 1 card from your hand to destroy 1 face-up Spell or Trap Card on your opponent's side of the field.
Destroying a face-up spell/trap isn't the best, but it can be helpful.
Run 1

YZ-Tank Dragon
"Y-Dragon Head" + "Z-Metal Tank"
This card cannot be Special Summoned except by removing from play the above monsters on your side of the field; then you can Special Summon this card from your Extra Deck (You do not use "Polymerization"). Discard 1 card from your hand to destroy 1 face-down Monster Card on your opponent's side of the field.
Destroying face-down monsters is pretty good.
Run 1

XZ-Tank Cannon
"X-Head Cannon" + "Z-Metal Tank"
This card cannot be Special Summoned except by banishing the above monsters on your side of the field; then you can Special Summon this card from your Extra Deck. (You do not use "Polymerization"). Discard 1 card from your hand to destroy 1 face-down Spell or Trap Card on your opponent's side of the field.
Much better then the previous two.
Run 1

VW-Tiger Catapult
"V-Tiger Jet" + "W-Wing Catapult"
This card can only be Special Summoned from your Extra Deck by banishing the above cards on your side of the field. (You do not use "Polymerization"). By discarding 1 card from your hand, change the battle position of 1 monster on your opponent's side of the field. (Flip Effects are not activated at this time.)
The effect isn't that great unfortunately, but if you're going for VWXYZ, you need to run this card.
Run 1-2

XYZ-Dragon Cannon
"X-Head Cannon" + "Y-Dragon Head" + "Z-Metal Tank"
This card can only be Special Summoned from your Extra Deck by removing from play the above cards you control. (You do not use "Polymerization".) This card cannot be Special Summoned from the Graveyard. You can discard 1 card to destroy 1 card your opponent controls.
Discard to destroy anything on the field? Now that's more like it. Amazing artwork. Only bad thing is its difficult to summon and can't be special summoned from the Graveyard.
Run 1-2

VWXYZ-Dragon Catapult Cannon
"VW-Tiger Catapult" + "XYZ-Dragon Cannon"
This card can only be Special Summoned from your Extra Deck by removing from play the above cards you control (You do not use "Polymerization"). Once per turn, remove from play 1 card your opponent controls. When this card attacks, you can change the battle position of the attack target. (Flip Effects are not activated at this time.)
I will admit, this card is really cool, but that doesn't make it good. You need a grand total of 7 monsters to summon this card! So unless you're super lucky, or your opponent is just bad, the chances of you summoning this guy successfully aren't very high. You're better off just running XYZ-Dragon Cannon instead. If you are playing a VWXYZ build;
Run 1
Spoiler:

Honest
During your Main Phase, you can return this card from the field to its owner's hand. During either player's Damage Step, when a face-up LIGHT monster you control battles, you can send this card from your hand to the Graveyard to have that monster gain ATK equal to the ATK of the opponent's monster it is battling, until the End Phase.
Honestly, this is an amazing card. All of your monsters are light, so you may as well.
Run 1

Cyber Eltanin
This card cannot be Normal Summoned or Set. This card cannot be Special Summoned except by removing from play all face-up LIGHT Machine-Type monsters from your side of the field and your Graveyard. This card's ATK and DEF are equal to the number of monsters removed from play for its Special Summon x 500. When this card is Special Summoned, send all other face-up monsters on the field to the Graveyard.
Again, your running lots of light monsters so this card is pretty good. This can also help combo with Cyber Network.
Run 0-1

Shining Angel
When this card is destroyed by battle and sent to the Graveyard: You can Special Summon 1 LIGHT monster with 1500 or less ATK from your Deck, in face-up Attack Position.
Decent searcher. Not really much else to say.
Run 0-2

Summoner Monk
This card cannot be Tributed. When this card is Normal or Flip Summoned, it is changed to Defense Position. Once per turn, you can discard 1 Spell Card to Special Summon 1 Level 4 monster from your Deck. It cannot attack this turn.
Not bad for this deck as all of your monsters are level 4.
Run 0-1

Morphing Jar
FLIP: Both players discard all the cards in their hands, then draw 5 cards.
This is a fantastic card for the deck. If you manage to get out XYZ-Dragon Cannon and have this face-down, you're going to have a lot of ammo to pull apart your opponents field.
Run 1

Jade Knight
Face-up Machine-Type monsters you control with 1200 or less ATK cannot be destroyed by the effects of Trap Cards. When this face-up card is destroyed by battle and sent to the Graveyard, you can add 1 Level 4 LIGHT Machine-Type monster from your Deck to your hand.
Pretty much a worse version of Shining Angel. Run it if you want.
Run 0-2

Elemental HERO Prisma
Once per turn: You can reveal 1 Fusion Monster from your Extra Deck, then send 1 of the Fusion Material Monsters listed on that card from your Main Deck to the Graveyard; this card's name becomes the sent monster's name until the End Phase.
Great card for the deck as you can fusion summon a lot easier using this card. Dumping a monster to the graveyard also combos really well with cards like Roll Out! You also have lots of different ways to search this card.
Run 2-3

Phantom of Chaos
Any Battle Damage your opponent takes from battles involving this card becomes 0. Once per turn: You can target 1 Effect Monster in your Graveyard; banish that target, then, until the End Phase, this card's name and ATK become that monster's name and ATK, and it gains that monster's effects. You must control this face-up card to activate and to resolve this effect.
Pretty good. You can copy a card from the graveyard and the fusion summon with it.
Run 0-2

Frontline Base
Once per turn, during your Main Phase, you can Special Summon 1 Level 4 or lower Union Monster from your hand.
Not a bad card. You can essentially summon twice per turn.
Run 0-2

Machina Armoured Unit
Once per turn, when a Machine-Type monster is destroyed by battle and sent to your Graveyard, you can Special Summon 1 Machine-Type monster with lower ATK and the same Attribute from your Deck.
This card can be really helpful with bringing all your fusion materials to the field. Use it if you want.
Run 0-2

Roll Out!
Select 1 Union Monster in your Graveyard and equip it to an appropriate monster you control
Fantastic card. If Call of the Haunted is ever limited, then this is the card you will want to use. Until then, run Call of the Haunted.
Run 0-2

Return from the Differant Dimension
Pay half your Life Points. Special Summon as many of your removed from play monsters as possible. During the End Phase, remove from play all monsters that were Special Summoned by this effect.
Although this card is now banned, it was fantastic for the deck. You pay half you life points, bring back all your fusion materials that were banished, and then get a free VWXYZ monster.

Cyber Network
Destroy this card during your 3rd Standby Phase after activation. Once per turn, if "Cyber Dragon" is on the field: You can banish 1 LIGHT Machine-Type monster from your Deck. When this card on the field is sent to the Graveyard: Special Summon as many of your banished LIGHT Machine-Type monsters as possible and destroy all Spell/Trap Cards you control. Those monsters cannot activate their effects. You cannot conduct your Battle Phase the turn you activate this effect.
This card is fantastic. Although you're going to have to run Cyber Dragon's, in 3 turns, you can banish all the parts you need, and then fusion summon for your big monsters. I would recommend running Cyber Dragon Core as it searches this card, as well as Cyber Dragon Drei is it will help keep Core alive when banished for Network.
Run 2-3
Quick Overview:
Machina's are an archetype consisting of EARTH attribute monsters. They were released with their own Structure Deck, Machina Mayhem. Although it is almost impossible to actually make a functioning Machina deck, when splashed into other decks such as Geargia or Gadgets, they can be very good.
Spoiler:

Machina Fortress
You can discard Machine-Type monster(s) whose total Levels equal 8 or more to Special Summon this card from your hand or Graveyard. When this card is destroyed by battle and sent to the Graveyard, select and destroy 1 card your opponent controls. When this face-up card you control is targeted by an opponent's Effect Monster's effect, look at your opponent's hand and discard 1 card from their hand.
This is hands down the best Machina card. It is super easy to summon as it can discard itself, and it is just a pain to get rid of.
Run 2-3

Machina Gearframe
When this card is Normal Summoned, you can add 1 "Machina" monster, except "Machina Gearframe", from your Deck to your hand. Once per turn, during your Main Phase, you can equip this card to a Machine-Type monster you control as an Equip Card, OR unequip it to Special Summon this card in face-up Attack Position. (A monster can only be equipped with 1 Union Monster at a time. If the equipped monster would be destroyed, destroy this card instead.)
Searches out basically everything in the archetype.
Run 3

Machina Peacekeeper
When this card on the field is destroyed and sent to the Graveyard, you can add 1 Union Monster from your Deck to your hand. Once per turn, during your Main Phase, you can equip this card to a Machine-Type monster you control as an Equip Card, OR unequip it to Special Summon this card in face-up Attack Position. (A monster can only be equipped with 1 Union Monster at a time. If the equipped monster would be destroyed, destroy this card instead.)
A decent card, not the best. It's better to put it in a deck that uses a lot of union monsters.
Run 0-2

Machina Force
This card cannot be Normal Summoned or Set. This card cannot be Special Summoned except with "Commander Covington". This card cannot declare an attack unless you pay 1000 Life Points. You can send this card from the field to the Graveyard to select and Special Summon one each of "Machina Soldier", "Machina Sniper", and "Machina Defender" from your Graveyard.
It's going to be very difficult to summon this guy, and it's not even really worth it. This cards main job was to be discard fodder for Machina Fortress, but then Machina Cannon came out.
Run 0

Machina Cannon
This card cannot be Normal Summoned or Set. This card can only Special Summoned by sending any number of Machine-Type monsters from your hand to the Graveyard. If this card is Special Summoned by its own effect, it gains 800 ATK for each monster sent to the Graveyard for its Special Summon.
The better Machina Fortress. It's better because it can actually be summoned if need be.
Run 1

Machina Armored Unit
Once per turn, when a Machine-Type monster is destroyed by battle and sent to your Graveyard, you can Special Summon 1 Machine-Type monster with lower ATK and the same Attribute from your Deck.
Pretty good card. It's very splashable. I have run this in Gadgets, and it's hilarious.
Run 0-2
Spoiler:

Commander Covington
You can send one face-up "Machina Soldier", "Machina Sniper", and "Machina Defender" you control to the Graveyard to Special Summon 1 "Machina Force" from your hand or your Deck.
Seeing as Machina Force isn't even that good, the cards used to summon it aren't good either. Don't run it. If you wanted to make a deck based around Machina Force though;
Run 1-2

Machina Soldier
When this card is Normal Summoned while you control no monsters, you can Special Summon 1 "Machina" monster from your hand, except "Machina Soldier".
Pretty good as it helps fill your field quicker for Commander Covington. Same deal as Covington though, don't use it unless you're running a Machina Force themed deck, and if so;
Run 2-3

Machina Sniper
"Machina" monsters cannot be attacked, except "Machina Sniper".
Summon Soldier, special Sniper. If you have a lot of backrow you might be able to pull Machina Force off with this. Don't use this card unless you're running a Machina Force themed deck, and if so;
Run 2

Machina Defender
FLIP: Add 1 "Commander Covington" from your Deck to your hand.
Searches Covington which is alright I guess. Don't use this card unless you're running a Machina Force themed deck, and if so;
Run 2
Quick Overview:
Meklords were...actually, I think Zero would do a better job at explaining this. Thanks for making life a little bit easier Zero

Spoiler: