The Man o' War is an enemy found in the Aquatic Depths biome. It jolts toward the player periodically to deal contact damage like other jellyfish enemies. In expert mode, it will occasionally become electrified. When it does so, it becomes invulnerable and maintains the velocity and direction it was initially traveling at also similar to other jellyfish.
The Man o' War has 2 more tentacles than vanilla Jellyfish.
The real life Portuguese man o' war's name comes from the man-of-war, a 16th to 19th century name for a powerful warship coined by the Royal Navy.