I found one that was really cool. On pg. 70 of the 1E DMG, it says:
Magically Sleeping or Held Opponents: If a general melee is in progress, and the attacker is subject to enemy attacks, then these opponents are automatically struck by any attack to which they would normally be subject, and the maximum damage possible according to weapon type is inflicted each time such an opponent is so attacked. The number of attacks or attack routines possible against such opponents is twice the number normally allowed in a round. Otherwise, such opponents may be automatically slain...
Ouch!
So if there is no active combat going on, the attacker can kill the sleeping/held opponent outright. Check. Everyone seems to remember that. However, the other part seems to have been forgotten at every forum in which it's ever been discussed, that I can recall.
The sleeping/held opponent, when being attacked by an attacker who is himself subject to attack (ie melee is still active), is automatically hit, the weapon automatically does max damage, and the attacker gets twice as many attacks as normal! Wow! This is just vicious!
A fighter who normally gets two attacks per round with his two-handed sword now gets four attacks that automatically hit for 40 pt damage in one round! Yikes!

A clay golem that is hasting itself that round gets 4 attacks, doing 120 pt damage that round!

An iron golem would do 160 pt damage!


Oh, I just gotta remember to use this rule, I really do!

Anyone else find some forgotten rules that are interesting?