Jeffy is one of the main characters from the YouTube Puppet Series, SuperMarioLogan. (SML)
He is a 20 year old boy (born August 21, 2004) who is the adopted son of Marvin (Mario) and Rose (Rosalina).
Jeffy can be described as stupid, malicious and dumb, but he can also show good behavior and smartness at times.
He was first introduced in the now deleted video titled "SML Movie: Mario The Babysitter" uploaded January 24th 2016. He is voiced and pupeteered by Lance Thirtyacre (Older brother of Logan Thirtyacre, who created SML).