I'd love to see a mechanic like this for the Dragoon, or something similar.

Lancet
Recast: 90s
Duration: 20s
Using certain actions while under the effect of Lancet will grant Decimate . Each unit of Decimate increases critical hit rate by 5%. When five units are stacked, you will become Enraged. All Decimate is lost when Lancet ends.

Heavens Dive
Recast 90s
Delivers an attack with a Potency of 500
Can only be executed when Enraged. All Decimate is lost when used.
Additional Effect: Increases target's damage taken by 10%
Duration: 10s

Actions that Grant Decimate:

Chaos Thrust, Full Thrust, Phlebotomize, Jump, Spineshatter Dive, Dragonfire Dive