Bridge Troll Guardian

Keen Smell. The troll has advantage on Wisdom (Perception) checks that rely on smell.

Regeneration. The troll regains 10 hit points at the start of its turn. If the troll takes acid or fire damage, this trait doesn't function at the start of the troll's next turn. The troll dies only if it starts its turn with 0 hit points and doesn't regenerate.

Bridge Guardian. The Troll Bridge Guardian has advantage on all rolls when it is within 30 feet of its bridge. Additionally, it can sense any creature within 60 feet of the bridge, even if the creature is hidden or invisible.

Multiattack. The troll makes three attacks: one with its bite and two with its claws or make one heave attack.

Bite. Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 12 (2d6 + 5) piercing damage.

Claw. Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 14 (2d8 + 5) bludgeoning damage.

Heave. The Troll Bridge Guardian picks up and throws a large rock or a similar object within 60 feet. It makes a ranged attack (+9 to hit) against a target, dealing 18 (2d12 + 5) bludgeoning damage on a hit.

Reactive Regeneration: 1/day:  In response to taking damage, the Troll Bridge Guardian can use its reaction to instantly regenerate 20 hit points