The first list I looked at was, of course, the Most Dangerous Creatures. What's more fun than seeing what's destroying your fellow players? Nothing. Nothing at all. It looks like Loken of Halls of Lightning is topping the charts right now, followed by Sapphiron of Naxxramas. I can see that. Loken can be pretty deadly, especially on Heroic. Most players will probably wipe to him at least once their first time seeing him, assuming they don't know the strategy ahead of time. Sapphiron is just plain painful.