In "License to Till", Mertz makes an appearance by showing up at a party, and is shown praising Steve, when he offers to drive members of the party to another party across town.
He tricks Steve and his friends into coming to one of his parties for the cool kids in "The Unincludeds", there they are egged. When they become prosperous in the future and invent a time machine, he steals one and returns to the past where he plants the idea for them to throw a party while posing as a janitor, which results in them becoming popular and ruining their future.
Mertz is impressed when Steve and his friends become witches in "The Witches of Langley".
Mertz is voiced by Judah Miller.