The Revenant
Bank the residual energy of everything you shoot, then wear it as a shroud: spectral claws that hit hardest up close.
The Revenant's shared reserve for protection, attack costs and time in Shroud. Capacity: 100; a run or new map starts with 45.
Outside Shroud, direct gun damage actually dealt adds 0.03 life force per damage; critical hits multiply that gain by 1.6. Overkill does not count.
Outside Shroud, an enemy dying within 15 m adds 3 life force. Siphon also builds the reserve.
In Shroud, Reaping Harvest and Soul Splinters can return life force after attack costs.