Quote Originally Posted by Slipperychicken View Post
It's like the massive damage rule.

It's so awful, and so universally ignored, nobody even knows it exists and is practically a variant rule.
Now now, the idea behind the massive damage rule is all right actually, but my DM tends to prefer to run it with being a specific amount of your characters total hp (think it's like half hp or above) to be considered "massive damage". The XP Penalty for multi-classing doesn't even have an "all right" basic idea going for it. :p