[Edi]

Life drain isn't negtaed by MR. You can find all the weapons MR protects against by looking at the Weapons DB and filtering out everything that doesn't have a value of TRUE in the mres column.

As for how to avoid horrors with a rainbow mage: Make sure you have astral magic and some astral gems and script the spell Returning. That'll get him out of the combat and leave only the possible bodyguards to be slaughtered.

Edi