Keen Hearing and Smell. The wolf has advantage on Wisdom (Perception) checks that rely on hearing or smell.

Petrifying Gaze (2/Day). If a creature starts its turn within 50 feet of the Ruin Guardian and the two of them can see each other, the Ruin Guardian can force the creature to make a DC 17 Constitution saving throw if the Ruin Guardian isn't incapacitated. On a failed save, the creature magically begins to turn to stone and is restrained. It must repeat the saving throw at the end of its next turn. On a success, the effect ends. On a failure, the creature is restrained until freed by the greater restoration spell or other magic.

A creature that isn't surprised can avert its eyes to avoid the saving throw at the start of its turn. If it does so, it can't see the Ruin Guardian until the start of its next turn, when it can avert its eyes again.

Multiattack. The Ruin Guardian makes three attacks; one Bite (Wolf Head) and two Bite (Snake Head) attacks.

Bite (Wolf Head). Melee Weapon Attack: +10 to hit, reach 5 ft., 1 target. Hit: 33 (8d6 + 5) piercing damage. 

Bite (Snake Head). Melee Weapon Attack: +11 to hit, range 20 ft., 1 target. Hit: 3(1d6) piercing and 25 (6d6 + 4) poison damage.