Chesnaught (5e Creature)
From D&D Wiki
Medium elemental, any alignment
Bulletproof. Ranged attacks have disadvantage against the chesnaught.
Overgrow. While it has 40 hit points or fewer, the chesnaught has advantage on attack rolls. In addition, it deals an extra 10 (3d6) damage to any target it hits with an attack.
Leech Seed. The chesnaught targets one creature within 60 feet of it that it can see. The target must make a DC 15 Constitution saving throw. On a successful save, the creature can't be targeted by the chesnaught's leech seed for 24 hours. On a failed save, the creature is infected by a leech seed. While infected in this way, a creature takes 9 (2d8) necrotic damage at the start of each of its turns, and the chesnaught regains the same number of hit points. A creature can repeat the saving throw at the end of each of its turns, ending the effect on a success. If the saving throw is successful or the effect ends for the creature, it can't be targeted by the chesnaught's leech seed for 24 hours.
Wood Hammer. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 27 (5d8 + 5) bludgeoning damage.
Spiky Shield. If a creature hits the chesnaught with a melee attack, it can use its reaction to deal 9 (2d8) piercing damage to the attacker.