Pokémon NetBattle was an online Pokémon battle simulator that covered the first three generations for competitive play. Its successor, NetBattle Supremacy, added further support and allowed the use of Pokémon from the fourth generation.
The program allows users to construct a team of Pokémon from the first three generations for competitive play. As a battle simulator, it allowed players to choose the known moves, held item, IVs, EVs, Nature, coloration, and Ability for their team. All Pokémon are assumed to be level 100 and any moves that can possibly be learned by that Pokémon are permitted. The program includes numerous helpful features, such as searchable Pokédex, moves and Abilities lists, a compatibility guide for Pokémon, and a table of weaknesses and resistances. It supports both Double Battles and a Stadium Mode, in which only three Pokémon from each team are used.
Also included are several "clauses," which are optional and limit the effectiveness of certain strategies. The Sleep Clause prevents more than one Pokémon from being asleep (excluding by Rest) on each team; likewise, a Freeze Clause prevents more than one Pokémon from being frozen on each team. The Self-KO Clause causes self-destructive moves (like Destiny Bond) to automatically fail if used by the last Pokémon for that team, in order to prevent ties. It also causes the user of Explosion or Selfdestruct in a 1-on-1 situation to lose the match (normally this results in a tie).
NetBattle used to be extremely popular in 2004 to 2006. However, starting around late 2007 to early 2008, the program's popularity started to decrease due to the release of Pokémon Diamond and Pearl.
On February 14, 2009, a newer version of NetBattle called NetBattle Supremacy was released by a programmer known as 'Bayleef'. NetBattle Supremacy added support for fourth generation Pokémon and feature.