Not sure if I missed it or if it hasn't been added to the thread yet- a boss spawns once you kill enough Ancient Cave Dwellers. Otherwise, thank you so much for this thread :) it's been really helpful

all lg bosses have an rng chance to spawn after each one of their specific elites you beat, but the % chance they will appear increases for each one you beat that they don't spawn.

So it could take you 20+ times beating one type of elite, or you could beat one elite, get their boss, beat their boss, fight the other of the two elites, and get the boss again

Yes I am aware of that- I was pointing out that, unlike the other spawnable bosses, Amarok doesn't have a description/battle guide posted on the one spawned from the ancient cave dwellers.

Hello, thank you for pointing that out. If I don't have a guide for some things yet its because I haven't been able to beat them or I just havent reached that part of the game yet. Some of these bosses are super tough!

How do you get the heart of the forest material? All you put was ???. Does it just randomly pop up for something?

At the time that post was written I do believe it was unknown how the item would be obtained, and I think Amarok's just not remembered to go back and edit that bit.
So I will clarify here that it's a one-off drop from the Grove Behemoth that you have to beat for stage 5- you can see it amongst the behemoth drops shown here

Thank you!

*cries in I need to know where Captain Rylak is in Stage 11, and am also very, very lost in the Caverns*

he's by the mysterious locked door in the same room where Demora Crystalheart spawns (the smallish room that's accessed via the door in the south wall of the cave's big main room, near the golem, in case you haven't ever met that particular boss)

updating it now >:-]