This promo aired on Nickelodeon during October 2010 and featured a short scene where Cosmo and Wanda, dressed in Frankenstein and his bride costumes, were making Poof eat broccoli before he could go trick-or-treating for candy.
Suddenly, Poof sees the full Halloween moon and turns into a zombie-cyclops monster. He starts eating the furniture in Timmy's house, and Cosmo says "You won't have enough space for candy if you fill up with furniture", so Poof eats him. Inside Poof, Cosmo says "I was wrong, there's plenty of room for candy!" and the bumper ends.
This promo appears to be an original short and not a clip from an actual episode.