Okay no stats except for speed and age. Every character starts with a single point in speed but through dark rituals or magical items can gain more. Every point of speed above 1 doubles your speed and halves your lifespan. So speed three makes you 4x fast, 1/4 lifespan, etc. Geometric progression.
At high speeds you get multiple actions per round and are harder to hit etc, but things like movement becomes weird and hard because friction is different when you work at that speed. Also you become disconnected from the world around you because it's harder and harder to communicate cause everyone seems to be sssssllloooooowwweeeeeedddd ddddoooowwwwnnnn
Sometimes there'd be enemies who were sped up even faster than the players and they'd have to deal with that in whatever way they could think of
And after the adventure they have to live out what days they have left at high speed, aging before their loved ones eyes