Alien

The Alien archetype is a Reptile-based strategy that wins by weakening and stealing the opponent's monsters through a mechanic unique to the archetype: A-Counters. Nearly every card in the deck either places these counters on opposing monsters or exploits them, since each A-Counter reduces a monster's ATK and DEF by 300 whenever it battles an Alien. Alien Dog accelerates the counter-placement process by Special Summoning itself from the hand whenever another Alien is Normal Summoned and immediately dropping two A-Counters onto opposing monsters, while Alien Warrior and Alien Stealthbuster contribute counters even in defeat, punishing the opponent for trading into them.

The deck's primary method of dismantling an opponent's board is theft rather than straightforward battle. Alien Hypno takes control of any counter-laden monster during the Main Phase and holds it for as long as A-Counters remain on it, while Brainwashing Beam provides a continuous Trap version of the same concept. Alien Mother pushes further by reviving whatever A-Counter monster it destroys in battle, effectively recruiting the opponent's own resources. "A" Cell Recombination Device ties the spell suite together, sending an Alien from the deck to the graveyard to load counters while setting up a search on a later turn.

Cosmic Fortress Gol'gar, the deck's Synchro anchor, demands Alien Ammonite as its Tuner and rewards that investment with the ability to bounce face-up Spells and Traps in exchange for additional A-Counter distribution, then spend those counters to destroy cards outright. Cosmic Slicer Zer'oll complements it from the Link side, locking countered monsters into Defence Position while searching any card that places A-Counters on summon.