RPGs have a lot of mechanics to help power their games. However, not all these mechanics work out as well as the designers intended. Some fail to do their job, or do their job but are more burdensome than helpful. Others are great fun, but maybe don't do what they were intended for? Some though, do the job and t hey do it well.
So what is your favorite?
For me, I think I have two.
The first is Raises. Raises is basically the system allowing the player to call their own critical hits. If you're good enough to do a task well, you can call raises and get more impact out of the GM. It's the difference between needing to hope for a mega good roll that is a low percentage chance of happening, and being able to make those moments happen when you want. Sure, it robs the joy of a nat 20 at the right moment, but it also lets you feel your character's superior skill when you can do things better than other people not because you luck out on the die roll, but because you can call more raises than them. You can find this mechanic in Legend of Five Rings and in the original 7th Sea.
The second is actually another John Wick game. It's the "team bond" mechanic found in The Aegis Project. The mechanic is simple: for every mission a PC has survived with the group they putt 1d6 into a communal pool (up to 5 max) at the beginning of the session. If the PC wants to keep some for themself that's fine too, but it's holding back from the group. Then, during play, any Player can pull one or more dice from that communal pool at any time (without group permission) and spend it to help with an action. At the end of the session, every unspent die is becomes an alotment of XP that gets evenly spread across the whole group. Remainder dice are lost.
I love this second mechanic because it very aptly represents a group cohesion in a stress situation. It makes the whole group feel it if someone dies, because suddenly Tom isn't dropping 5 dice into the pool anymore. He's dropping 0. Only, Tom is still spending from the pool, and Tom's new character is still getting a fair cut of the bonus XP even though he didn't put anything in to it. Which means you also get the feel of the FNG and having to accomodate getting this new person not only into the squad, but meshing with the other members.
It's a wonderful mechanic, and one I try to use anytime I'm doing a war game where the idea is the story of a squad.
How about you?