What Game Mechanic inspires your play the most?
For the past 13 years, the game mechanic that has inspired me the most are Aspects, from the Fate system designed by Fred Hicks and Rob Donoghue.
An Aspect is a word or phrase that describes something special about a person, place, thing, situation, or group. Almost anything you can think of can have aspects. A character might be the Fastest Gun In The Galaxy. A room might be On Fire after you knock over an oil lamp. After you are wounded in combat, you might have a Sprained Ankle. Aspects let you change the story in ways that go along with your character’s tendencies, skills, or problems.
You spend points during play to activate an aspect and have it effect the game (via bonuses or penalties to die rolls, etc.), and can earn points by allowing aspects to complicate your character’s life. (For example, the GM might give you points if they decide that your Fastest Gun in the Galaxy aspect means that an NPC has heard of you and wants to challenge you to a showdown!)
They pretty much perfectly suit the sort of narrative influence on game play that I prefer, and, thanks to the decision to declare the Fate system Open Content via the Open Gaming License, you are free to include them in your own designs. They are so much a part of how I think about RPG play that they’ve featured in every design I’ve worked on in the past decade.