Troll and I

Like the game as a whole, this boss was very glitchy for my wife & I, with Otto dying on random jumps being the most irritating. This took us several hours to finish as a result. However, here's a list of what you need to do, and I'll add a helpful glitch at the end in spoiler tags that helped us out, for anyone interested. I'm adding it at the end in case some of you don't want to exploit the glitch.

For the helmet, Otto needs 3 green tip spears to remove the first section, 3 green tip spears to remove the second section, 1 green tip spear & 1 red tip spear to destroy the remainder of his helmet. Don't pay any attention to the colors, this is exactly how we did it. Just aim for the center of his head, it doesn't matter if it's flashing a color or where as long as you hit him in the head.

For the shield covering the boss' stomach, Troll needs to throw 2 boulders to break the first half off & 3 boulders to break the second half off. Boulders are located behind 2 rock walls, one on the left in front of the boss & one on the right opposite where the magic rune is.

After all of the armor has been destroyed, use Otto to make your way up to jump on the boss' head. You'll need to follow the path from where the green shards & spears are, jump one gap & then when you're slightly behind the boss' left shoulder jump another gap, be sure you have some stamina otherwise Otto may fall down the gap & die. After you make it across there are 2 small enemies to kill. Keep following the path around, circling around the boss. You'll come to some blue shards & spears, collect them if you need them. Directly in front of you is a wall Otto can climb. Climb up with the prompt but not over. You'll see an enemy that throws spears up ahead. Wait for him to turn his back then climb up, running up to him to catch him off guard & engage him in combat. If he sees Otto with enough distance he will throw a spear, something that you don't want because if he hits you, the spears kill Otto instantly. You can perhaps kill him with a red tip spear as well, but it might be more risky & I'm not sure if a single spear is powerful enough to kill him as we never tried. With this deadly enemy disposed of, continue following the path around & you will happen upon 3 more small enemies. Kill them & continue on, there will be another gap here but if you fall down you can recover & make your way back up. You will jump across one final gap into 2 large warrior enemies & 3 small enemies. You can kill them easily & are now able to jump on the boss' head. Make sure Troll is ready with a boulder before you jump.

Jump onto his head with the prompt & using Troll aim the boulder with & throw it at the exposed stomach with . There won't be enough time to throw another boulder & Otto will jump off the boss' head, you'll simply need to run up the circular path again (which is why disposing of the enemies the first time is important), jump on the boss' head again, and throw a boulder at his stomach again. That's it, in a quick anticlimactic slump the boss is finished.

Here are some tips that may be useful:

There is a cavern behind you at the start of the battle, make sure Otto goes into it & grabs some weapon bindings & shards in a small pocket to the left if you didn't notice it before the battle began.

There are green shards & spears to pick up above the rune Troll draws power from, to the right of where you start the boss battle. We were not able to locate any red shards until you destroy the Ahky's helmet so it would be best to keep this in mind & bring some in to battle.

Any time you break a piece of the boss's armor off enemies crawl out of the ground, it's easiest to pound them with Troll. If Otto is short weapon bindings to craft spears they usually drop at least a few. Keep hitting the boss in the stomach & they will continue to crawl out until you have enough bindings.

Here is the glitch we found: