I think that making it "Receive max HP equal to the monster's level" would be much simpler
2xmonster level max HP for 3-4 piety might work out interestingly.
@Lujo, just tested it: Human Paladin of Dracul on Hexx Ruins, half-prepped (smugglers, prepped god, dragon shield, though that wasn't too important)... cheeky, unstoppable, ding, specialist, warmonger, parched. Potions unconverted, ton of bloodpools left, piety banked up, had 1 lifesteal from Dracul + 1 from vamp sword and 3 sanguine I think. Used no swells. Vampire Dungeon went unused.
Second boss was Tomithy, whom I flattened at level 5 or 6 with health restoration alone.
Now, that's not a good drac dungeon : p
Attempt the second - Warmonger Parched Dinging etc. (Unstoppable - I didn't get the badge, not sure why but if I missed something I could've killed it) Human Drac Paladin on Magma Mines. Whurgarbl instead of Dragon Shield. Losing the resistances made the early game trickier (got 2 lifesteals instead of Blood Shield) but the late game was still a happy rollover.