Jellyfish are passive Mobs found in the Shipwrecked DLC. They float around in the shallow Ocean, sometimes in groups. New ones will spawn every 60 seconds to replace those who are lost. They will not attack the player if they are approached, but if they are attacked with a melee Weapon, they will automatically shock the player, doing 5 points of Health damage. They will not actively attack the player. Once killed, their carcass will float in the water until picked up.
Jellyfish can also be caught alive using a Net or a Trawl Net, or killed safely when equipped with an item that provides electrical resistance (such as the Snakeskin Hat or Snakeskin Jacket). As inventory items, they can be murdered by right-clicking them to produce Dead Jellyfish, which can be eaten to restore 10 and 10 , making them a great way to restore Hunger and Health at sea. A Jellyfish placed on the ground will immediately turn into a Dead Jellyfish. They will have a short animation where they flop twice before settling like any normal Dead Jellyfish.
A Jellyfish can be cooked to make Cooked Jellyfish, while Dead Jellyfish can be dried on a Drying Rack to acquire Dried Jellyfish. Jellyfish can be used in the Crock Pot, they count as 1 unit of Fishes and 1 unit of Monster.
Jellyfish take 2 blasts from the Ice Staff to be frozen and 1 Sleep Dart to be put to sleep. They are considered innocent creatures, and killing one adds 1 point to the player's naughtiness level, which can cause Krampus to appear.
- If the player is using a weapon that deals more than 50 damage, such as a fresh Ham Bat, The player can kill a Jellyfish in one hit, meaning they will only take 5 damage without protection from the shock. Because eating a dead Jellyfish restores 10 Health, it means the player can gain 5 Health very easily. Because of how common Jellyfish are, it is a good tactic to restore Health fairly quickly.
- The bodily appearance of the Jellyfish, and the fact they can be eaten, suggests that they are modeled after Rhizostomae order of Jellyfish, which is mostly composed of edible Jellyfishes.
- Jellyfish are the only mobs that can cause direct health damage to the player while they are on a Boat.
- Jellyfish are the only shipwrecked-only food that counts as both fish and monster.
- Real life Jellyfish do not cause an electric shock. Instead they inject poison to their victim on contact, which is described with feeling similar to electrocution.