Reactive: The tentacle trap can take a reaction on every turn in a combat.
Constrict. Melee Weapon Attack: +5 to hit, reach 10 ft., one target. Hit: 13 (2d8 + 4) bludgeoning damage, and the target is grappled (escape DC 14). Until this grapple ends, the target is restrained, and the tentacle trap can't constrict another target.
Swift Grasp. If a creature moves within 10 feet of the tentacle trap, it can use its reaction to make a Constrict attack against that creature.