Pipe cleaner Dom was first seen in strip [139].
Ph34r my l33t pip3 h4ir! = Fear my leet pipe hair!
The Vibrating Sheep is from strip [119], though it was originally of Death instead of Doom.
Play Doh - the popular modeling clay
Gumby - the old stop-motion clay television show
Dom's rant confirms: "I had nothing to do with this one. Honestly. This is all Fred."