I hit it first and it hit me back and it hit me so hard that it took away around 75% of my health. So I back off, cast a healing spell, get close to the beast and when it rises its claw to hit me again I step back, it swings at the air and I hit it, but I barely hurt it. It took me several hits to bring the troll's health close to 25% and then... it healed itself. I realized this wasn't going anywhere so I repeated the hit-n-run tactic but this time when it prepared to heal itself again I shouted a fus roh dah at it and stunned it. After a few more minutes it was dead.
This lasted so long that I went up two levels during this fight alone (I kid you not).
