Shark

The Shark is an aquatic creature that deals 40 damage, has 300 health, and is VERY resistant to knockback. It can easily kill a player who is unprepared for it.

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Due to their wide hitbox and the surrounding water slowing projectiles, Sharks are highly susceptible to piercing attacks, as they can potentially damage the Shark multiple times. Flails are particularly effective, with a single well-aimed, well-timed attack scoring up to five hits with ease.

Tips
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 * The fastest way to get a diving helmet is to set up a Shark Trap, like the one shown in the video above. A space of 8x2, Sharks and Jellyfish have no trouble beaching themselves on the lava shelf. By having the wooden platforms at the water level, the lava won't eat through it. Then you simply stand in a little pool of water inside the house to attract all the sharks and Jellyfish you could ever want while you remain safe inside.
 * Another way is to build a long string of platforms across the top of the ocean. Float around and bait a shark towards you, then use your grappling hook to pull yourself up to the platforms and out of the water. As the shark swims back in to the murky depths, bombarde it with explosives. Sharks will die from 4-6 grenades usually.
 * In 1.1 It is rare.
 * Sharks do not spawn in Corrupted or Hallowed Oceans. If your oceans have been corrupted or hallowed, bring along some Purification/Vile Powder.