Chasm

Story related; cannot be missed.

King Trell is the final boss in the Keep. He will slash-combo with his sword, spawn skeleton archers, send out energy waves, unleash a spin attack, and throw shurikens at you. The arena is wide, so if he spawns an archer, you can run away to isolate King Trell from his minion, making them a bit easier to deal with. Upon killing him, this trophy will unlock.