Black and Purple Troll

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.

Loathsome Limbs. Whenever the troll takes at least 15 slashing damage at one time, roll a d20 to determine what else happens to it:

1–10: Nothing else happens.

11–14: One leg is severed from the troll if it has any legs left.

15–18: One arm is severed from the troll if it has any arms left.

19–20: The troll is decapitated, but the troll dies only if it can’t regenerate. If it dies, so does the severed head.

If the troll finishes a short or long rest without reattaching a severed limb or head, the part regrows. At that point, the severed part dies. Until then, a severed part acts on the troll’s initiative and has its own action and movement. A severed part has AC 13, 10 hit points, and the troll’s Regeneration trait.

A severed leg is unable to attack and has a speed of 5 feet.

A severed arm has a speed of 5 feet and can make one claw attack on its turn, with disadvantage on the attack roll unless the troll can see the arm and its target. Each time the troll loses an arm, it loses a claw attack.

If its head is severed, the troll loses its bite attack and its body is blinded unless the head can see it. The severed head has a speed of 0 feet and the troll’s Keen Smell trait. It can make a bite attack but only against a target in its space.

The troll’s speed is halved if it’s missing a leg. If it loses both legs, it falls prone. If it has both arms, it can crawl. With only one arm, it can still crawl, but its speed is halved. With no arms or legs, its speed is 0, and it can’t benefit from bonuses to speed.

Amphibious. The dragon can breathe air and water.

Legendary Resistance (3/Day). If the dragon fails a saving throw, it can choose to succeed instead.

Tunneler. The worm can burrow through solid rock at half its burrow speed and leaves a 10-foot-diameter tunnel in its wake.

Multiattack. The troll makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +11 to hit, reach 10 ft., one target. Hit: 17 (2d10 + 6) piercing damage plus 4 (1d8) acid damage.

Claw. Melee Weapon Attack: +11 to hit, reach 5 ft., one target. Hit: 13 (2d6 + 6) slashing damage.

Tail Stinger. Melee Weapon Attack: +14 to hit, reach 10 ft., one creature. Hit: 19 (3d6 + 9) piercing damage, and the target must make a DC 19 Constitution saving throw, taking 42 (12d6) poison damage on a failed save, or half as much damage on a successful one.

Tail. Melee Weapon Attack: +11 to hit, reach 15 ft., one target. Hit: 15 (2d8 + 6) bludgeoning damage.

Acid Breath (Recharge 5–6). The dragon exhales acid in a 60-­foot line that is 5 feet wide. Each creature in that line must make a DC 18 Dexterity saving throw, taking 54 (12d8) acid damage on a failed save, or half as much damage on a successful one.

The dragon can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The dragon regains spent legendary actions at the start of its turn.

Detect. The dragon makes a Wisdom (Perception) check.

Tail Attack. The dragon makes a tail attack.

Wing Attack (Costs 2 Actions). The dragon beats its wings. Each creature within 10 feet of the dragon must succeed on a DC 19 Dexterity saving throw or take 13 (2d6 + 6) bludgeoning damage and be knocked prone. The dragon can then fly up to half its flying speed.