https://www.pokecheck.org/?screenshot=8571143&la
This Chikorita inside a Nest Ball is marked as having a Valid Pokéball. However, based on
it appears that it should only be able come with a regular Pokéball since it is an NPC gift. Is the legality checker showing false negatives in this case? Similarly, this Cyndaquil and Totodile also have alternate balls appear as valid.