ToME: the Tales of Maj'Eyal

Using vim has become somewhat more difficult in the last few versions: with no respawning monsterns anymore, you can't just nip into a nearby dungeon to top off your tank, and with drain no longer being usable on yourself, that exploit isn't available anymore either. Sacrifice only works when you have more than 40% of your HP, and as it is you really should only use it when you're at full health.

I believe sacrifice could use a bit more flexibility and cost 40% of your current health instead of 40% of your max. That way it would be always usable (as long as there's and enemy in sight - maybe make that a mobile enemy?). Also it would become cheaper in relative terms when wounded, yet more risky since it will leave you at even less health absolutely.

For boss fights, drain could be boosted if the vim recovered were multiplied by the target's rank.

Good ideas done

I recommend also having them regenerate Vim in the overworld the same way Equilibrium recovers there -- assume that they're hunting for food or whatever off-screen if you want. It's not hard to find someplace to recover your vim (especially if you deliberately leave a low level dungeon full of monsters so you can go there and use sacrifice), but it seems silly to actually force them to do that.