Well, how i leveled them up is:
1. Go to tormenta a healer would be nice.
2. Treasure room is good, there's also an advantage... you might have a chance of getting a legendary weapon!
3. Oh and watch out... if you kill an enemy and they drop a loot pouch, loot chest, or loot skull chest, they might be far and you won't see your treasure. Watch out for that!
