Many creepypasta ROM hacks (like Pokémon Lost Silver or Pokémon 764 ) claim to be "cursed" cartridges found from a time before the game actually existed.
that combine Pokémon with Ultraman or original monsters, some exist on forums like PokeCommunity or ROM hacking sites. However, sharing or downloading copyrighted ROMs is illegal, and I can't provide direct links or promote piracy.
1986PokemonEmeraldUTrashMan directory listing - Internet Archive
(Generations 1–7), Mega Evolutions, and multiple regions including Johto, Kanto, and the Orange Islands. Key Features of Ultra Shiny Gold Sigma