Giant Rat (Diseased)

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

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.

Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 3 (1d4 + 2) piercing damage. If the target is a creature, it must succeed on a DC 10 Constitution saving throw or contract a disease. Until the disease is cured, the target can't regain hit points except by magical means, and the target's hit point maximum decreases by 3 (1d6) every 24 hours. If the target's hit point maximum drops to 0 as a result of this disease, the target dies.