Cadaverous Appearance. While the zombie dog is lying still, it is indistinguishable from a mundane decomposing corpse. It can still be detected by a detect evil and good spell, or similar magic.

Keen Smell. The zombie dog has advantage on Wisdom (Perception) checks that rely on smell.

Pounce. If the zombie dog moves at least 15 feet directly toward a creature, and then hits it with a bite attack on the same turn, the target must succeed on a DC 12 Strength saving throw, or be knocked prone.

Undead Fortitude. If damage reduces the zombie to 0 hit points, it must make a Constitution saving throw with a DC of 5 + the damage taken, unless the damage is radiant or from a critical hit. On a success, the zombie drops to 1 hit point instead.

Bite. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 4 (1d6 + 2) piercing damage.