Multiattack. The grell makes two attacks: one with its tentacles and one with its beak.
Tentacles. Melee Weapon Attack: +4 to hit, reach 10 ft., one creature. Hit: 7 (1d10 + 2) piercing damage, and the target must succeed on a DC: 11 Constitution saving throw or be poisoned for 1 minute. The poisoned target is paralyzed, and it can repeat the saving throw at the end of each of its turns, ending the effect on a success.
Beak. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 7 (2d4 + 2) piercing damage.