Three-Headed. The dog has advantage on Wisdom (Perception) checks and on saving throws against being blinded, charmed, deafened, frightened, stunned, or knocked unconscious.

Incessant yapping. The chihuahua cerberus never stops yapping unless it is asleep. Any creature that can hear its yapping for over 1d4-1 rounds must make a DC 12 Constitution saving throw or take 3d4 psychic damage. If the creature succeeds three times in a row than they are immune to this effect for one hour. If the creature takes 10 or more damage from this trait in one round than they must make another DC 12 Wisdom Saving throw or gain an effect from the short-term madness table.

Multiattack. The dog makes three bite attacks.

Bite. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 5 (1d4+ 3) 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.