"Gadget" (ガジェット Gajetto) is an archetype of Machine monsters (with the exception of the Cyberse "Cyberse Gadget" and "Gadget Token").
The primary "Gadget" monsters and their support focus on generic Machine support, fast Summoning and swarming, and are centred around the cards "Green Gadget", "Red Gadget", and "Yellow Gadget", used by Yugi Muto. These Gadgets also synergise strongly with the "Ancient Gear" archetype, due to several members of the latter archetype directly supporting the colored Gadgets or Gadgets in general. There is also a smaller group of "Gadget" monsters that support the "Morphtronic" archetype, and are used by Leo in the anime, as well as a few others which do not belong to either group.
"Green Gadget" appears as a character in Yu-Gi-Oh! Ultimate Masters: World Championship Tournament 2006, in World Championship 2007, in World Championship 2008, in World Championship 2009, in World Championship 2010, and in Duel Arena.
The most common way to play "Gadget" archetype is to use it with "Machina" cards. A Machina Gadget deck focuses on bringing out "Machina Fortress" and/or Rank 4 Xyz Monsters on to the field, generating a constant stream of Gadget monsters through "Red", "Green" and "Yellow Gadget" and maintaining advantage over the opponent. With the advent of "Gold Gadget and Silver Gadget, the player can get another "Gadget" monster on to the field more quickly.
While this Deck can be strong, cards like "System Down" and "Acid Rain" will destroy all three "Gadgets" and all "A-to-Z" monsters. "Malfunction", "Mystical Space Typhoon", "Royal Decree", and "Trap Reactor・Y FI" (which also inflicts burn damage) would prevent "Stronghold the Moving Fortress" from appearing in the field. Sliding cards like "Imperial Order" and "Imperial Custom" (try to get this card out instead) can counter these cards.