Pack Tactics. The abyssal rat has advantage on an attack roll against a creature if at least one of the rat's allies is within 5 feet of the creature and the ally isn't incapacitated.

Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., 1 target. Hit: 3 (1d4 + 1) piercing damage. Creatures hit with this attack must make a DC 10 constitution saving throw or take 10 (3d6) poison damage and be poisoned for 1 minute, targets can repeat the saving throw at the end of each of their turns.