Mickey Mouse Seacrest is the host of American Idol Mario Edition. As the series went on, it is revealed that Mickey Seacrest was not the real host, but he continues to return (in hiding from an angry Mr. Pig).
Although it is unknown what happened to him after his disappearance from the series, it can be assumed that he was arrested for being a fake host on national television. He was mentioned years later on American Idol: Season 2, Episode 1. He hasn't made an appearance ever since.
The Mickey Seacrest character make an obvious pun off of real-life American Idol host, Ryan Seacrest.
The paired Minnie plush appeared in Mario And Tony: Happy New Year
He has never appeared in any new episodes. It is most likely that the plush was Logan's parent's, as the plush comes with a minnie plush as well, and was a wedding gift, and Logan couldn't take it to the apartment or the new house, where season 2 is set in.