mario and Yoshi is a Gameboy game that isn't there how do I add it

According to Wikipedia, Mario & Yoshi and the game named Yoshi are the same game. It is called Mario & Yoshi in Europe and Australia

https://en.wikipedia.org/wiki/Yoshi(video_game)

Yoshi - http://completionator.com/Game/Details/2095

I'm going to leave it up to moho if a separate entry be added for Mario & Yoshi or just load the Europe box art for Yoshi to match.

For now I updated the alias so Yoshi pops up when someone types Mario & Yoshi

If you come across more games that are missing please post here and we'll get them added: http://completionator.com/Forum/PostList/6?page=1

I agree, this one appears to be the same game, just with different regional names.