Pokemon.wad is a WAD file that brings Pokémon into ZDoom and Skulltag. It has several Generation I and II Pokémon in place of the normal Doom monsters. Maps, similarly, are based on towns, routes, and dungeons from the first two sets of Pokémon games, though, excluding the path through the Pokémon world taken, the games' storylines are mostly skimmed over. The protagonist is still Doomguy, trying to make his way out from the Pokémon world. The mod started development in 2002 and was last updated in 2012.
Doom Wiki