Just as he did in 2011, Ren & Stimpy creator John Kricfalusi has lent his animation talents to The Simpsons, providing a spooky musical couch gag for this year’s “Treehouse of Horror†episode. It’s a little bit Hanna-Barbera, a little bit Nightmare Before Christmas, and 100 percent freaky, fretful, and frightening. But check out the name on the pivotal gravestone, and wonder if the gruesome violence on display isn’t some sort of karmic rebalancing.