The drain life spell heals you with some of the HP you drained from your target, possibly even increasing maximum HP by one point if it is full (though this is probably too powerful).

The healing isn’t intended for anyone who can cast it; it would require you to have a certain amount of attack skill and possibly be chaotic.

Vampires drain levels much less than they currently do, or not at all; instead they use a bite with an AD_DRHP damage type (described in #1627). Possibly give vampires one AD_DRHP attack but let vampire lords keep one AD_DRHP and one AD_DRLI.

Mosquitoes, an a-class monster which uses an AD_DRHP attack, which replenishes the mosquito’s health by some fraction of the damage it dealt you.

Clerical spell that gives you a certain duration of a property that steals enemies’ maxHP and heals you when you hit things in melee.

Attempting to move healers out of the petmastering role: they now have skilled medical knowledge that enables them to hit monsters in melee with a scalpel or knife to inflict a “bleeding” status effect which will cause the monster to lose HP continuously. Any role is able to do this with a scalpel, but the effect is much more limited than it is for Healers. This means that for a Healer, combat now consists of hitting a monster to make it bleed, then disengaging and keeping away from it in the hope that it dies on its own. The Staff of Aesculapius no longer drains, instead it heals the damage it would have dealt (unless the Cyclops has it, in which case it drains life like normal.)

Additionally, the Staff of Aesculapius no longer has level-draining powers. Instead it has a drain HP attack that heals the wielder.