The Portuguese man o’war can be found in warm salt water, floating on the surface as it trails its poisonous tentacles below. The poison of a man o’war inflicts damage and paralysis, though a saving throw vs poison negates the latter. Creatures succumbing to the man o’war venom are drawn up to the body of the creature and consumed in 3d4 turns. The delicate tentacles can be broken by inflicting 1 hp damage upon them, but this does not hurt the man o’war and the tentacle regrows in 1d3 days. Only damage to the body of the Portuguese man o’war can kill it. Though the man o’war floats on the surface of the water, the creature breathes water and will suffocate if removed from the sea.

Portuguese men o’war comprise a large body dominated by a huge flotation sac and a number of long slender tentacles that trail beneath it in the water. The man o’war’s flotation sac is translucent and is unlikely to be seen 90% of the time unless the being encountering them can see invisible. The size of the man o’war and the number of its tentacles is determined by its HD. The man o’war’s body will be 2½-ft in diameter for every HD. Thus a 1 HD man o’war will be 2½-ft in diameter and a 3 HD man o’war 7½-ft in diameter. The number and length of its tentacles also vary by HD; there will be ten tentacles per HD, and ten ft of length per HD. Thus, a 3 HD Portuguese man o’war will have 30 tentacles, each of which are 30-ft long.