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Armor Class 15 (natural armor)

Hit Points 105 (10d10+50)

Speed 50 ft.

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Saving Throws Str +9, Con +8

Skills Perception +5, Stealth +6

Condition Immunities frightened

Senses darkvision 30 ft., passive Perception 15

Challenge 7 (2,900 XP)

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Ambush Predator. If the Thornback surprises a creature and hits it with an attack during the first round of combat, the target takes an extra 21 (6d6) damage from the attack.

Spine Defense. Any creature that grapples the Thornback or hits it with a melee attack within 5 feet takes 7 (2d6) piercing damage from its calcified spines.

Multileg Stability. The Thornback has advantage on saving throws against being knocked prone. It cannot be knocked prone by effects that affect two-legged creatures' balance.

Keen Senses. The Thornback has advantage on Wisdom (Perception) checks that rely on smell or hearing.

Actions

Multiattack. The Thornback makes two attacks: one with its bite and one with its spine rake.

Bite. Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 22 (3d10+6) piercing damage and the target is grappled (escape DC 17). While grappled, the target is restrained and the Thornback can't bite a different target.

Spine Rake. Melee Weapon Attack: +9 to hit, reach 5 ft., one target not grappled by the Thornback. Hit: 20 (4d6+6) piercing damage. On a hit, the target's speed is halved until the end of its next turn.

Spine Volley (Recharge 5-6). The Thornback launches a burst of spines in a 30-foot cone. Each creature in that area must make a DC 17 Dexterity saving throw, taking 28 (8d6) piercing damage on a failed save or half on a success. Creatures that fail the save also have their speed halved until the end of their next turn.