Pokémon Infinite Fusion is really great! It’s Pokémon but you can fuse two monsters together to make a new one. A lot of the fusions have custom art! (The other ones are like that old Pokémon fusion creator that pastes one monster’s face over the other one, lol.)

Look for their Discord if you want to download it. All websites that profess to have download links are unofficial and may be malicious.