Yeah, so something like this would be neat:

First revert Dark Passenger, then -

Dark Arts:
Attune with the darkness within you, increasing the potency of several actions. Can only be executed when succumbing to the Darkside. Effect fades if Darkside is canceled.
Duration: 10s
Additional Effect: Reduces the recast timer of Carve and Spit and Dark Passenger by 1 second.

The Blackest Night: Creates a barrier around self that absorbs damage totaling 20% of your maximum HP, or around a party member that absorbs damage totaling 10% of your maximum HP.
Duration: 6s
Increases Blood Gauge by 50 when full 20% (10%) is absorbed.
Additional Effect: Reduces the recast timer of Delirium and Shadow Wall by 5 seconds when full 20% (10%) is absorbed.