[Snake]

Silvermists
Consumes 33% of your current Essence and restores HP equal to 3 per Essence, to a minimum of 25. Any excess HP will be converted into FP instead.

A percentage healing like a PR-Hi Potion would make this a little too absurd, due to how tanks are seen. I think everybody would prefer SAN being a defining factor to it. So how about:

Silvermists
Consumes 25% of your current Essence, restores 9 HP per 1 Essence consumed ([strike]plus 8% of your maximum HP, if Lunar Lunatism is active)[/strike], to a minimum of 25. It has a 2 round cooldown.

Vampires have every sorts of non-Vampire skill healings reduced by 75%, they're outmatched with survivability. Added to how stupid Holy enchant is on them, and at how Interference can be a giant nuisance at all times.

Not even Dullahans are having so much trouble with sustaining themselves in battle, and they can't even drink potions.

Edit: No %