Critical Miss house rules. The most common version is that if you roll a natural 1, you lose the remaining attacks that you have for that round, or have to roll on a chart that involves many very bad options (drop your weapon, break your weapon, hurt yourself, take some sort of penalty until next turn, etc). This strongly penalizes people who add more attacks per round. For example, a Totemist who has 10 attacks (not hard to accomplish by mid levels) will generally have a critical miss every other round. Critical Hit house rules tend to be equally ridiculous for the opposite reason, making perfectly acceptable Tier 3ish classes that make one attack per round a lot weaker.