Alien

The Aliens are a series of Reptile-Type cards introduced in "Power of the Duelist", with further support added in "Cyberdark Impact", "Strike of Neos", "Force of the Breaker, "Tactical Evolution, "Gladiator's Assault", "Crimson Crisis" and "Raging Battle". Alien decks focus heavily on the use of "A-Counters", which weaken opposing monsters battling Aliens and allow the Alien user to take control of them. This is the first true Reptile archetype and one of the only archetypes that focuses heavily on manipulating the opponent.

Playing style
Aliens focus on manipulating the opponent rather than strengthening themselves. They have a wide range of lower-level monsters that can be used to oppress or manipulate the opponent but are lacking at higher levels; however, the ability to take control of or weaken opponents' strong monsters more than makes up for this deficiency. That being said, the new cards from "Crimson Crisis" have made aliens much stronger due to the powerful field-clearing effect of "Cosmic Fortress Gol'gar" and the rapid A-Counter distribution of "Alien Overlord", as well as the devastating force of "Planet Pollutant Virus", which wipes out any of your opponent's monsters without A-Counters and infects any they summon for the next three turns. And with the new addition of "Alien Dog" from "Raging Battle", Aliens are capable of swarming the field easily.

As "Crimson Crisis" and "Raging Battle" have added a variety of support for Alien monsters, there are many different deck and playing styles for Aliens. The Alien cards before "Crimson Crisis" focused combining A-Counter distribution, lower-level effect monsters, and monster manipulation. As such, Alien users should be aware of the strengths of "playing small" by utilizing "weaker" Alien effect monsters, such as Alien Mars and Alien Psychic. However, Aliens currently possess a relatively large number of low-level beatdown monsters ("Alien Warrior" and "Alien Shocktrooper"), each of which are powerful enough to devastate your opponent with little help. "Alien Warrior" in particular will weaken opponent monsters with A-Counters on them, effectively allowing it to destroy powerful cards such as Jinzo and the Monarchs; and, in the event that "Alien Warrior" is destroyed in battle, it will distribute a good number of A-Counters to ensure that whatever follows will have a distinct advantage.

It should be noted that no monster in the Alien archetype has over 2600 ATK, and the two strongest monsters in the archetype ("Cosmic Horror Gangi'el" and "Cosmic Fortress Gol'gar", considered as the "Boss Monsters" of the Aliens) technically do not count as "Aliens", and thus do not weaken opponents monsters with A-Counters during battle. However, "Cosmic Fortress Gol'gar" can destroy opponent's monsters by removing 2 A-Counters from the field."Cosmic Horror Gangi'el" does in fact have the "weaken opponents monsters with A-Counters during battle"

All Alien decks in some way require A-Counters to be truly effective. An Alien deck that swarms quickly needs A-Counters to summon Alien Overlord and A-Counters to use "Code A Ancient Ruins". Alien decks that take control of opponents monsters through cards such as Alien Hypno, Brainwashing Beam, and Mass Hypnosis require A-Counters on opponents monsters to control them. A-Counters also are a part of battle as well-- as many Alien monsters have the stacking effect of reducing opponent's monsters' Attack and Defense by 300 points for each counter on the opponent's monster(s).

For a swarming strategy, "Code A Ancient Ruins" is easily abused with the effect of "Cosmic Fortress Gol'gar". By having multiple Code A Ancient Ruins and Cosmic Fortress Gol'gars on the field, you can use Gol'gar's effect to return the Ruins to your hand, producing more A-Counters and allowing you to use Ruins once more, which then lets you swarm the field quickly, or even Synchro Summon even more monsters by recycling "Alien Ammonite".

Weaknesses
The major weakness Alien decks have is that against decks that swarm can keep your Aliens from putting "A" Counters on them fast enough. Alien Kid, Alien Warrior, and Planet Pollutant Virus are a few ways to keep up with swarming strategies. They're also incredibly weak to "Skill Drain" decks, which will completely take away the field advantage Aliens need to have to abuse monsters with "A" counters. Also Remove Brainwashing could severely damage this deck by taking away the ability of manipulating your opponent's monsters. "Macro Cosmos" and "Dimensional Fissure" can be harmful as well, as they almost render the effects of "Code A Ancient Ruins" and "Alien Ammonite" useless.

A-Counters


Putting A-Counters on opposing cards is essential to the success of Alien decks, as Aliens generally have no extremely powerful monsters other than "Cosmic Horror Gangi'el" and "Cosmic Fortress Gol'gar".

Since counters cannot be placed on face-down monsters, generally the best way to ensure that A-Counters can be used against the opponent is to use "Light of Intervention", though note that doing so negates much of the usefulness of "Alien Grey". Another use for "Light of Intervention" is that when Tribute Summoning "Flying Saucer Muusik'i" it can be Summoned in face-up defense position, creating a temporary barrier and allowing you to use its effect during your next Draw Phase. Other alternatives include "Ceasefire" or "Swords of Revealing Light".

According to the current ruling in A-Counters, the effect of decreasing the ATK and DEF of monsters in battling with Alien monsters is applied regardless to whether or not there is a monster on the field with that effect; therefore, these effects are not accumulative. If you control an Alien Shocktrooper the ATK of a monster battling with it that can A-Counters will still loose ATK and DEF; summarily, if you control multiple copies of Alien Overlord, the loss of ATK and DEF is not multiplied.