Rillaboom (5e Creature)
From D&D Wiki
Medium plant, any alignment
Grassy Surge. A creature that hits the rillaboom with a melee attack while within 5 feet of it must succeed on a DC 17 Strength saving throw or be restrained by a surge of plants for 1 minute. It can repeat the saving throw at the end of each of its turns, ending the effect on a success.
Overgrow. While it has 50 hit points or fewer, the rillaboom has advantage on attack rolls. In addition, it deals an extra 7 (2d6) damage to any target it hits with an attack.
Powerful Build. While grappling, the rillaboom is considered to be Large, and it is considered to be large for the purpose of determining carrying capacity.
Multiattack. The rillaboom makes two wood hammer attacks.
Wood Hammer. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 19 (4d6 + 5) bludgeoning damage.
Grassy Glide. The rillaboom moves up to its speed in a straight line, including through other creature's space during this move, it ignores difficult terrain composed of plants. Each creature whose space it moves through must make a DC 14 Dexterity saving throw. A creature takes 18 (3d8 + 5) bludgeoning damage on a failed save, or half as much on a successful one. Whether it succeeds or fails, it is pushed to an unoccupied space within 5 ft. of the line. If no unoccupied space is within range, the creature instead falls prone in its space. The area the rillaboom moves through becomes difficult terrain as grass begins to grow wildly.
Drum Beating (Recharge 5-6). One creature within 60 feet of the rillaboom that it can see must succeed on a DC 15 Strength saving throw or take 27 (6d8) bludgeoning damage and be restrained by overgrown grass for 1 minute. While restrained in this way, the target takes 9 (2d8) bludgeoning damage at the start of each of its turns. The target can repeat the saving throw at the end of each of its turns, ending the effect on a success.