Arkham Horror already is great at making you go insane (inside the game, that is. It, hopefully, doesn't make you go insane outside of the game. I mean, it's a good game. I wouldn't expect playing it to actually cause you to lose sanity). With the new Grave Consequences expansion, though, insanity is almost guaranteed (once again, inside the game. Not outside). It's available now.
So what do you get in this mind-bending expansion? 50 cards broken up into the Phobia, Epic Battles, and Epitaph decks. The Phobia deck will eat away at your sanity every time their conditions are met. The Epic Battles deck adds even more challenge to your battles against the Old Once, giving them a new ability every turn. Finally, the Epitaph deck is for when your investigator doesn't make it out alive. It could be a help or a hindrance, but once your character kicks the bucket, they go into effect.