From Homestar Runner Wiki
Each year since 2007, The Brothers Chaps released Halloween teasers, which display a message saying that the Halloween toon will be put on the site later on. In every teaser, Strong Bad has on a ridiculously realistic costume and it's never the same in the real toon. Also in every teaser, one can decompile the Flash file to see words written behind the silhouettes. There is always some action that occurs after waiting, and the teaser links back to the Halloween-themed Main Page 7. There was no teaser in 2010, as there was no accompanying toon.
 The Teasers
 The Hidden Images
Big toons: Homestarloween Party (costumes) | The House That Gave Sucky Treats (costumes) | Pumpkin Carve-nival (costumes) | 3 Times Halloween Funjob (costumes) | Halloween Fairstival (costumes) | Halloween Potion-ma-jig (costumes) | Happy Hallow-day (costumes) | Jibblies 2 (costumes) | Most in the Graveyard (costumes) | Doomy Tales of the Macabre (costumes) | Which Ween Costumes? (costumes)