Gol-Hevel

The Murdered Guardian of the Second Gate; Gol-Hevel is one of the Grave Ruins Colossal Titans you'll come across in Titan Souls.

Tips for Beating
You'll need to target his back. He'll move in a pretty predictable diagonal around the room, so if you leave the arrow in a spot you can just withdraw it when he passes.

To quickly kill this boss, engage him from the left side and preemptively run all the way to the left middle pillar, then draw back your arrow to kill him before he even attacks.