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

Pounce. If the demon moves at least 20 feet straight toward a creature and then hits it with a claw attack on the same turn, that target must succeed on a DC 12 Strength saving throw or be knocked prone. If the target is prone, the demon can make one bite attack against it as a bonus action.

Pack Tactics. The demon has advantage on an attack roll against a creature if at least one of the demon's allies is within 5 feet of the creature and the ally isn't incapcitated.

The Zolveth demon makes two attacks, one with its bite and one with its claws.

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

Claw. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: (1d4 + 2) slashing damage.

Parry. The demon adds 3 to its AC against one melee attack that would hit it. To do so, the demon must see the attacker.