The player?

Not so sure, killed the clone in the grove of reflection with no problems, yes it's easy to kill a pure mage with a spell containing silence and weakness to magic, shock damage and weakness

The AI is pretty clueless, it had strong reflect spell potions
Gatekeeper and even more the second gatekeeper was hard to kill but not very dangerous as it had to reach you to do damage. Mended flesh elementals has my vote, immune against poison and with spell reflection, unlike the lich they are fast and hit hard.
OT: I has never understood the problem with cliffracers, they was not very hard to kill but you needed some sort of ranged attack bows, spells or cast on use damage on target. If you used damage speed 100 on target it was no reason to kill them