The Pokémon Series has a few Easter Eggs that appear in certain Nintendo-created games. They rarely appeared in the Super Mario franchise.
In Super Mario Galaxy, there is a planet in one of the Galaxy levels that appears to be in an Easter Egg form of a Poké Ball. That is also something that Pokémon Trainers use to capture new Pokémon creatures and train them. In Super Mario Maker, Bulbasaur, Charmander, and Squirtle were temporarily available for you to unlock from I Choose You! Event Course before the Nintendo Network Services died out after April 6, 2026. These Costume Mario characters should have been obtained by then. The only Pokémon characters that are no longer possible to unlock from 100 Mario Challenge but can still be obtained via amiibo are the following: Pikachu, Charizard, Jigglypuff, Lucario, Greninja, and, of course, Mewtwo.
In Yoshi’s Woolly World, it is possible to scan Pokémon amiibo into the game. However, you will only receive an amiibo-designed Yarn Yoshi.