Alien

The Aliens are a series of cards that were introduced in Power of the Duelist with new support recently added in Gladiator's Assault and Light of Destruction. The Alien's effects usually include placing "A-Counters" on opposing monsters to weaken the opponent's monster by 300 ATK and DEF.

Most Alien decks use the opponent's monsters as Tributes for your own and revolve heavily around Monster Control with the help of A-Counters. Since A-Counters cannot be placed on face-down monsters, a Trap Card that works in your favor in this case would be "Light of Intervention", since this prevents your opponent from setting monsters in face-down Defense Position. Also Aliens focus on stealing your opponent's monsters and using them for sacrifices for either Alien Mother or Cosmic Horror Gangi'el. This is one of the only kinds of decks that focus on this, making them sometimes very annoying to play against.

Play Style
Aliens require a high degree of skill to use properly, since they 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 an opponent's strong monster more than makes up for this deficiency. Duels involving Aliens tend to be a unique experience for both players due to how quickly the balance of power can shift during the duel, depending on how each player responds. Also, be sure to note that aliens are also reptiles, and can be supported with cards like Snake Whistle.

Appearance
Aesthetically, they are based on two sets of popular alien conspiracy theories: the "Roswell Grays" in Area 51 (for the "lower" Aliens) and the Reptilian Humanoid alien conspiracy (for Alien Hunter, Alien Warrior, Alien Shocktrooper, and Alien Mother); the second conspiracy may also have influenced the Alien's type as being Reptile, instead of Fiend or Fairy like other alien-like monsters such as Greed Quasar and Zeta Reticulant.

Most of the aliens have orbs, coloured according to their attribute, on their bodies.

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 (which does not strictly count as an "Alien").

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 the usefulness of Alien Grey. Some Alien users also use partial stalling effects like Vengeful Bog Spirit or Stumbling to ensure that they have enough time to place A-Counters on the opponent's monsters during their own turn.

According to the current ruling on A-Counters, they do not reduce the ATK and DEF of monsters battling Alien monsters if no cards exist on the field that mention that effect. This means that if you only control an Alien Shocktrooper, for example, your opponent's monsters will not be weakened no matter how many A-Counters are on them. The upside to this ruling, however, is that these effects stack, so if you control two Alien Warriors, the opponent's monsters will be twice as weakened for every A-Counter on them.

==  'Alien Brainwash Synchro!!!!!!!' ==

Why wouldn't anyone thinks of combining alien with synchro? Using alien's super enemy control ability,you can control your opponents high level monster. Then summon your own added tuner monster,it turns up a super synchro monster. [Cosmic Horror Gangi'el]and Alien Mother can collect free non-tuner monster. [Brain washing beam] and [Mass Hypnosis] also turns your opponent favorite monster into a super terror ultimate synchro monster!!! HA!!HA!!HA!!HA!!HA!!HA!!HA!!HA!!HA!!HA!!HA!!HA!!HA!!HA!!HA!!HA!!HA!!HA!!