Multiattack. The Grassulk makes four pincer attacks. Magic Drain. An enemy that starts its turn while grappled with the Grassulk's Vine Wrap (and is a spellcaster), must make a DC 13 Wisdom saving throw. On a failed save, the target looses 1 first level spell slot. The creature must make this save for every turn they begin grappled by the Grasshulk. On a successful save, the creature is immune to the effects of the Grassulk's Magic Drain for 24 hours.
Pincer. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 14 (2d6 +5) slashing damage. Vine Wrap. The Grasshulk targets 1 creature that they can sense within 30 ft. of it. The vines flowing from its back attempt to grapple the target. The creature can choose between a DC 14 Strength (Athletics) check or Dexterity (Acrobatics) check to resist. On a failed check, the target takes 11 (2d6) piercing damage from the vine's thorns, and is considered grappled.
The Grassulk can take 3 legendary actions per day. Only one legendary action can be used at a time and only at the end of another creatures turn. Spore Born. The Grassulk births 3 mushromm spores of the Elder Evil. These sentient mushroom spore creatures immediately attack any opponent of the Grassulk within 120 feet. Once the spores are within 5 ft. of their target, they will self-destruct sending spore dust into a 10 ft. radius. The target of the attack must make a DC 16 Dexterity saving throw. On a failed save, the creature is caught in the middle of the spore dust, sending their consciousness into the astral place. There they witness the horror of the Elder Evil itself, causing 25 (5d8) psychic damage before returning to the material plane. If a creature is caught in the blast of 2 or more spores, they make a single saving throw at disadvantage, and are only effected by the Elder Evil once.