Acrobatic bite. Instead of using their strength for their bite attack they use their dexterity. 

Keen smell. The abyssal dire rat has advantage on Wisdom (Perception) checks that rely on smell.

Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., 1 target. Hit: 5 (1d4 + 3) piercing damage and if the target isn't a construct, fiend or undead they must make a dc 13 Constitution saving throw or be diseased for 3 days each day that targets Constitution and Dexterity stats are reduced by 1d4 past those days it becomes permanent until the disease is cured.