Pokémon : The Hodgepodge Platoon

Hodgepodge Platoon is a Pokémon ROM Hack featuring 80+ usable Fakemon. The gameplay mostly consists of rental Pokémon battles in the HP Platoon facility, with a Battle Swap ruleset very akin to Pokémon Emerald's Battle Factory. The protagonist, Tawila, aims to see all there is to see in this realm, and show off in battle along the way. You'll be faced with brand new moves, abilities, stat spreads, and more, spanning all 9 generations of Pokémon. All of the playable Fakemon are lovingly designed and sprited by over 20 different artists. Hop on in and try to get the biggest streak, and fill out the Pokédex along the way!

Source: TheGamesDB