The Goblin
From Homestar Runner Wiki
The Goblin is a green creature who appears in Halloween episodes. An organ tune plays when he shows up, and he does a short dance. The movement of his feet when dancing is very similar to Leg Movement #1 in the Dancin' Bubs game.
The Goblin was created when Homestar Runner started telling a pass-along Halloween story in Homestarloween Party. He seems to make guest appearances in almost all Halloween episodes (the only major Halloween specials he has not appeared in so far are The House That Gave Sucky Treats and Halloween Fairstival).
By virtue of Bubs's addition to the pass-along story, he is also the owner of a '73 Gremlin. He's found hanging out under it in the Spooky Woods in Where's The Cheat?. According to the Horrible Painting, he has "serious problems", and Rocoulm refuses to entertain him.