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The Treasure Knight is the boss of the Iron Whale Stage.
This boss makes use of the giant harpoon attached to his arm to launch himself across the arena, usually straight at you. You’ll have to avoid both his harpoon and Treasure Knight himself as he closes the gap. As he leaps across the room to hit you, get in a drop hit with your shovel to help make quicker work of him. The boss will even shoot the harpoon up into the air to thwart your pogo attacks, and downwards when he jumps above you. When low on health, Treasure Knight will throw a chest into the middle of the arena, but don’t be fooled. a whirlpool will form at the chest, so avoid it at all costs, and dodge the bombs he tosses into the whirlpool. Make use of your relics to strike at different angles, and he will fall.