With Nintendo stating the PokeBank will be supported for Sun & Moon, many tried bringing their Red/Yellow/Blue Pokemon to the title (as the VC versions of those three games support PokeBank). One infamous Pokemon called ‘MissingNo.’ was still present in the VC releases and curious gamers tried bringing this buggy Pokemon to future games.
Sadly, this causes issues. As covered in the above IGN News Video, the Pokemon is messing up stats and more when placed in the PokeBank. It’s highly recommended you do NOT transfer your MissingNo. into the PokeBank, as you risk messing up your entire collection of Pokemon.