How does APHEELSIK work?

As an Assassin in Desktop Dungeons I'm trying to use the APHEELSIK glyph to help me kill higher level monsters. The game says APHEELSIK:

Poisons an enemy, negating health regeneration until player next deals damage.

So after attacking a zombie a few times I get low health and use APHEELSIK on the zombie. I assume that I can explore to regenerate health and mana well the zombie stays wounded (because I'm only exploring, not dealing damage) but then I come back and the zombie is fully regenerated!

So how does one use APHEELSIK in order to prevent monsters from regenerating health while you explore? Have I completely misinterpreted how to use APHEELSIK? Are certain monsters immune?

Solution 1:

The problem is not in how you are using APHEELSIK, but in your target. Normally, you would use APHEELSIK in a battle where both you and the target monster have taken a reasonable amount of damage. By casting APHEELSIK on a monster, you decrease its ability to heal from things that would normally heal both you and wounded monsters (exploration and use of LEMMISI). In the free version healing is prevented completely, while in the full version it is decreased by your level (so if the monster is 2 levels higher than you, it still heals 2 points per square).

However, Undead are immune:

Casting APHEELSIK on a Wraith, Zombie or Vampire will not inflict Poison on them, and thus has no effect on their Health Regeneration. It will still cost you Mana to cast the Glyph despite having no effect.

and some other creatures (like the Golem and Goat) can resist poison

The Golem and Goat, with their significant Magic Resistance, are poor targets for APHEELSIK. There is a chance for the spell to fail equal to the monster's Magic Resistance score. So, for instance, a Goat (with 25% Magic Resistance) will be able to resist APHEELSIK 25% of the time on average. When resisted, APHEELSIK does not inflict Poison on the monster.