How to Get the Burrower Larva
Second level of Lava mines!
Off in the right direction. Same deal with the three door fight.
He’s actually a bit of a pushover. I had harder fights getting to him. On the plus side that makes him a great fight for the “kill a 1-2 skull monster solo”, a few flasks and you get that medal (he’s repeatable so you can fight him as much as you want).
Note: If running solo quest on him, make sure to bring pots. The 150 damage ones work wonders. Every time he goes hiding he gets a buff that makes him stronger and you weaker.
By the time he gets 3 stacks he gets pretty powerful and you get pretty weak. Don’t let the fight go so long.