How do you deal with enemies with higher than 100% elemental resistances?
I waited a little bit to fight the Slugs, so when I fought them I had two water wands, Hail Strike, and Winter Blast. Rain + Global Cooling also snuffs out the fire trails because the ice just turns into water as they cross it.
Assuming DOS2 has major elemental places like DOS1 (Fire Undead, Winter Plane), you've got a couple of options:
1) Double Wands and freezing them, if you can outdamage their healing this way.
2) Put on resistance items, so their self healing is minimal. Then kill them the ordinary way.
3) Use your stockpiled scrolls. I had a mountain of scrolls I could use.
4) Lead them into a Barrel Trap. This is a little tedious, but lets you kill everything but Fire Immunes.
5) Pick up Necromancy for Decaying Touch.
The main reason why I didn't go with Necromancy was just a lack of spare points. In the real game (especially with Lone Wolf) I would definitely recommend at least a point of Necromancy. Decaying Touch absolutely wrecks enemies that your Retaliation would heal.