Well, Dark Green hunchback frackle, the one that appeared in the first episode when other Frackles besides Boppity, and Gloat, where not there, have appeared on Sesame Street, with out the mean eyebrows. You can see him in the skit with Bip Boppita, along with Frazzle, Cookie, and Herry, and some Anythings, but before the monsters, Guy Smiley, Prarie Dawn, and Simon Soundman are in it as well.
The puppets are probably very well worn out... They've been around since the early seventies. And Thog is probably gone. They could use a bully monster Gang on Sesame Street, to try and bully Telly, Grover, Herry, Cookie, Elmo, and the others. But you know, Elmo saves the day and what not.