Keen Smell. The rat has advantage on Wisdom (Perception) checks that rely on smell.
Pack Tactics. The rat has advantage on an attack roll against a creature if at least one of the rat's allies is within 5 ft. of the creature and the ally isn't incapacitated.
Actions
Bite. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 4 (1d4 + 2) piercing damage.