The Sea Snake
The Sea Snake is found in the last part in The Sea. It shoots magical orbs at you (doing roughly 100 damage per orb). It is impossible to kill, and spawns after every 1-3 sharks. The easiest way to avoid dying from the orbs is to swim all the way up or down, have the Unicorn Horn and the pink enchanted gloves to heal you, and have 1000+ health.