Nintendo would have some legal rights here, but I'm not that worried. Especially with more popular things like Pokerogue still existing. I've seen a number of fan games with Pokémon lookalike characters. As long as they don't say Pokémon, trainer, types, pokeball, etc, they should be fine. Nintendo doesn't typically sue smaller unmonetized content, they send warnings and threats, which can be ignored because it wastes too much of their money to properly sue.