Death Dog is a Medium monstrosity with neutral evil alignment and Challenge Rating 1 in the 2014 SRD. This stat block includes AC 12, 39 hit points, speeds, traits, and actions.
Multiattack - The dog makes two bite attacks.
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 must succeed on a DC 12 Constitution saving throw against disease or become poisoned until the disease is cured. Every 24 hours that elapse, the creature must repeat the saving throw, reducing its hit point maximum by 5 (1d10) on a failure. This reduction lasts until the disease is cured. The creature dies if the disease reduces its hit point maximum to 0.