While they always introduce a little bit of humor in every episode, every know and then they throw in one that's totally off the wall. Any ones with the trickster were awesome and you can't forget the one about the Chinese wishing well and the cursed coin.
The image of that giant depressed Teddy Bear complaining about the world was completely unexpected. These episodes are great to release a little tension that has been building up throughout the season. Supernatural is a pretty heavy show and tackles some pretty big issues. Dean spawns a daughter and she has to die. The brothers lose their father. Death and destruction is a part of the Supernatural universe.
The humor episodes are pretty common every now in then almost every television show. The last season of Supernatural was pretty heavy and depressing. The brothers were at odds and depressed as they faced off against an seemingly unbeatable enemy. The leviathans wants nothing less than total world domination and even the episodes that were meant to be funny were weighed down by it.
I think that last season will go down in history as the series' worst...at least I hope future ones aren't that bad. They need to make things fun again every now and then. The clown one was funny, but it just couldn't shake the off the season's woes. I hope the next season sees a shift away from the more painful and depressing to more fun and lighthearted like the first few seasons.
I now know that Season 8 will not be its last, so I hope the writers take the hint and create a new storyline that gives everyone a little hope.