I was able to unlock this my first try with help from Fuzzy Bearbarian on YouTube. Check out his video for a visual guide.
Use your sword and shield for this fight.
When the fight starts, get a medium distance between you and Luce, and then throw a few spears at him
. This should stun him (aim for his gut) briefly, run in
and hit him with 2 or 3 light attacks
and dodge backwards
. Repeat this a few times until he begin spewing purple crap at you. Strafe around this and move in, once he stops spewing, he is momentarily stunned. Get 2 or 3 hits in, backout.
Repeat this until he is at half health, he will now start rolling at you. Fuzzy doesnt do this, but simply standing behind an ice pillar will stun him, no need to strafe dodge. This will get you about 5 hits in make it count.
He will also start healing, you can tell this because he will make a kinda sumo pose, where he braces himself by planting one foot into the ground, throw a spear at him to stun him for a second or two.
Repeat and he should be dead in under 120 seconds.