OverUsed

OverUsed, or OU, is Smogon's standard tier. The highest level of play is generally seen in this tier, and it is the basis for all other tiers. The most powerful Pokémon are banned from this tier up to Ubers. Pokémon cannot rise from OU to Ubers based on usage. Most of the cover legendaries in addition to select other Pokémon are on the banlist.
Play Restrictions

   1: Endless Battle Clause: Any moveset on any Pokémon that is capable of intentionally causing an endless battle is banned from competitive play. Thus:
       - A Pokémon may not carry Recycle and hold a Leppa Berry in conjunction with Heal Pulse and Milk Drink, Moonlight, Morning Sun, Recover, Roost, Slack Off, Soft-Boiled, or Wish.
      -  A Pokémon may not hold a Leppa Berry and carry Recycle and Pain Split on its moveset.
       - A Pokémon may not hold a Leppa Berry and carry Recycle and Fling on its moveset.
   2: Baton Pass Clause: Only one Pokémon per team may know the move Baton Pass.
   3: Evasion Clause: The moves Double Team and Minimize are not permitted in play.
   4: Moody Clause: Pokémon with the ability Moody are not permitted.
   5: OHKO Clause: A Pokémon may not have the moves Fissure, Guillotine, Horn Drill, or Sheer Cold in its moveset.
   6: Sleep Clause: Only one Pokémon may be put to sleep on the opposing team at a time, if not induced by a move such as Rest.
   7: Species Clause: Players cannot have two Pokémon with the same Pokédex number on the same team.
   8: Pokémon may be up to level 100.

Banned Pokémon

    Aegislash
    Arceus
    Blaziken
    Darkrai
    Deoxys
    Deoxys-A
    Deoxys-D
    Deoxys-S
    Dialga
    Genesect
    Giratina
    Giratina-O
    Greninja
    Groudon
    Ho-Oh
    Kyogre
    Kyurem-W
    Lugia
    Mewtwo
    Palkia
    Rayquaza
    Reshiram
    Shaymin-S
    Xerneas
    Yveltal
    Zekrom

Banned Items

    Gengarite
    Kangaskhanite
    Lucarionite
    Mawilite
    Salamencite
    Soul Dew

Banned Moves

    Swagger