What are your favourite single game mechanics?

[GMMichael]

As a runner up...and this is probably cheating... would be my own "3d12 HMC Tables". Short version: You roll 3 different coloured dice...a 'bright/light/hot' one, a 'medium colour/neutral tone' one, and a 'dark/cold' one (Hot Medium Cold...HMC). The tables are colour coded, with a sort of cross-reference system to find the particular 'result/cell'.

Put these on a Rubik's Cube and I'll try it.

 

[The Crimson Binome]

One of my favorite new mechanics is the Wounded condition from Pathfinder 2. It's nice to see something to disincentive the use negligible healing to pop someone back up strategy. You should want to get them back in good shape.

On that note, I still really like (negative) Hit Points, because they also solve this problem. If you're barely down, and someone uses negligible healing to get you up again, then you're going to drop down even further from the next hit; and negligible healing might not be enough to get you up again after that.

Really, the more I think about it, the better Hit Points are as a mechanic. The do so much, with so little effort.

 

[aramis erak]

The Arcanum.

Armor as damage-reduction.

Changed my mind as a GM.

The Arcanum is, amongst many of my friends, thought of fondly as, "Palladium's mechanics redone by sane people."

The simpler combat mechanics, the much reduced HP gain, the ability to add skills when you see fit (provided you don't spend enough to lose a level)...