Death Dog

Two Heads. The death dog has advantage on Perception checks and on saving throws made to resist being blinded, charmed, deafened, frightened, stunned, or knocked unconscious, and it can't be flanked.

Multiattack. The death dog attacks twice with its bite.

Bite. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 5 (1d6+2) piercing damage. If the target is a creature it makes a DC 12 Constitution saving throw. On a failure it becomes infected with a disease. Until this disease is cured the target is poisoned. While diseased the target makes a DC 12 Constitution saving throw every 24 hours reducing its hit point maximum by 5 (1d10) on a failure and ending the disease on a success. This hit point maximum reduction lasts until the disease is cured. The target dies if its hit point maximum is reduced to 0.