Brood Mother

Keen Smell. The Brood Mother 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 Brood Mother's allies is within 5 feet of the creature and the ally isn't incapacitated.

Stench. Any creature other than a Brood Mother or a rat that starts its turn within 10 feet of the Brood Mother must succeed on a DC 14 Constitution saving throw or be [condition]poisoned[/condtion] until the start of the creature’s next turn. On a successful saving throw, the creature is immune to the stench of all Brood Mother's for 1 hour.

Multiattack. The Brood Mother makes 2 attacks. one with its Diseased fang, the other with its sharpened claws.

Diseased Fang. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 8 (1d8 + 3) piercing damage plus an extra 4 (1d8) poison damage. If the target is a creature, it must succeed on a DC 14 Constitution saving throw or contract a disease and become poisoned. 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 7 (2d6) every 24 hours. If the target’s hit point maximum drops to 0 as a result of this disease, the target dies. if the target successes on the saving throw the creature isn't poisoned and is immune to the disease for the next 24 hours.

Sharpened Claws. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 10 (2d6+3) slashing damage. plus an extra 2 (1d4) poison damage

Screeching Call. as a bonus action, the Brood Mother can direct another rat within 30ft of her to make an attack on a creature within 5ft of that rat. this spends the reaction of the Rat in question.