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Invertebrate, Monstrous Seastar

Large beast, unaligned

Armor Class 15 (natural armor)
Hit Points 104 (11d10 + 44)
Speed 10 ft., climb 10 ft.

17 (+3) 15 (+2) 18 (+4) 8 (-1) 13 (+1) 8 (-1)

Saving Throws Dex +5, Wis +4, Cha +2
Condition Immunities prone
Damage Resistances bludgeoning
Senses blindsight 30 ft., passive Perception 11
Challenge 6 (2,300 XP)


  • Tube Feet. Monstrous seastars move and grapple using thousands of shorter appendages filled with fluid and ending in tiny suctions cups. They treat any solid surface as clear terrain.
  • Regeneration. The seastar regains 5 hit points at the start of its turn. If the seastar takes acid or fire damage, this trait doesn’t function at the start of the seastar’s next turn. The seastar dies only if it starts its turn with 0 hit points and doesn’t regenerate.
  • Water Breathing. The seastar can breathe only underwater.


  • Multiattack. The seastar makes two slam attacks.
  • Slam. Melee Weapon Attack: +6 to hit, reach 15 ft., one target. Hit: 14 (2d10 + 3) bludgeoning damage, and if the target is a Medium or smaller creature and the seastar isn’t already grappling a creature, it is grappled (escape DC 12).
  • External Stomach. A seastar ejects its stomach in order to begin digestion of a captured meal. If the target is a Medium or smaller creature grappled by the seastar, that creature is digested, and the grapple ends. While being digested, the creature is blinded and restrained, it has total cover against attacks and other effects outside the seastar’s external stomach, and it takes 14 (4d6) acid damage at the start of each of the seastar’s turns. If the seastar’s external stomach takes 20 damage or more on a single turn from a creature inside it, the seastar must succeed on a DC 14 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, which fall prone in a space within 5 feet of the seastar. Damage done to a seastar’s stomach does not harm the seastar. If the seastar dies, a swallowed creature is no longer restrained by it and can escape from the corpse using 5 feet of movement, exiting prone.


  • Split. When a seastar is subjected to a critical hit from a slashing attack, it splits into two new seastars if it has at least 10 hit points. Each new seastar has hit points equal to half the original seastar’s, rounded down. New seastars are one size smaller than the original seastar.


When a monstrous seastar emerges from repose, muscular tentacles explode from the sand and fold inward toward its toothless central maw. These aggressive starfish average 7 to 10 feet in diameter and weigh 600 to 1000 pounds.

Creeping Doom. Starfish on some alien ocean worlds contend with a greater number of more dangerous marine threats than on other worlds. Their resulting evolution produced faster, stronger specimens that recover from injury very quickly. Most unique among the species is that some giant seastars have no agenda or reproductive mechanism other than to split and regenerate after being attacked by predators. Ironically, the number of natural enemies that find them delicious ensures their survival.

One Too Many Mouths. Monstrous seastars have mouths on both sides of their bodies, allowing them to crawl towards stationary food, or to lie half-buried in sand to ambush prey crawling across the seabed above them.

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Legendary Planet Adventure Path (5E) © 2020, Legendary Games; Authors: Matt Goodall, Jim Groves, Steven T. Helt, Tim Hitchcock, Jason Nelson, Richard Pett, Tom Phillips, Mike Shel, Neil Spicer, Mike D. Welham