I just re-read an old post-
I saw a comment in my favorite meta-thread a week or so ago that, roughly boiled down, was, "Yo. AD&D wasn't that difficult. Heck, combat was much less lethal than later editions like 5e. AD&D was practically easy mode. By fourth level, you really couldn't die in AD&D." Now, when I first read...
www.enworld.org
It reminded me of my favorite "obscure" rule...
SYSTEM SHOCK!!!!
To recap, system shock rolls (part of constitution) were the percentage chance that you died when certain things happen.
Little known applications-
1. If the party magic user polymorphs you, you had to save TWICE, once when you were polymorphed, and once when you came back.
2. It applied to all aging affects; that's right, in addition to haste aging you, it had a chance to KILL YOU every time it was used. This also applied when you cast wish, gate, etc.
DM: So, Fizwalter the Slightly Dumb, you cast wish! What do you wish for?
Player: I wish that this spell didn't age me and kill me.