I decided I wanted to give this a try. I found a couple of Reddit posts and You tube videos on the subject. A couple used devouring swarm and another used canister bomb. I decided to go a different direction. I used summon brairthorn.
It worked very well. I leveled about half way on the island for some better gear than ran past most things on the way. The briarthorn killed enough on the way there to get me to level 10. Was lucky enough to buy 1 Subjugator ring on the way. That probably saved a little time in the fight. One thing to remember is that since you’re not doing a lot of killing on the way, you may be short of healing potions. Before the fight you may want to spend what little iron you have on healing potions. Hope this helps others who might be interested in going for that achievement.
I have never been interested in achievements, but I guess a 16/16 Grenado build would work.