Clockwork Sphinx

Inscrutable. The sphinx is immune to any effect that would sense its emotions or read its thoughts, as well as any divination spell that it refuses. Wisdom (Insight) checks made to ascertain the sphinx's intentions or sincerity have disadvantage.

Multiattack. The sphinx makes two claw attacks.

Claw. Melee Weapon Attack: +12 to hit, reach 5 ft., one target. Hit: 17 (2d10 + 6) slashing damage.

Acid Spray (Recharge 5-6). Ranged Weapon Attack: +5 to hit, range 20/30 ft., one target. Hit: 10 (2d6) acid damage. 

Roar (3/Day). The sphinx emits a magical roar. Each time it roars before finishing a long rest, the roar is louder and the effect is different, as detailed below. Each creature within 500 feet of the sphinx and able to hear the roar must make a saving throw.

First Roar. Each creature that fails a DC 18 Wisdom saving throw is frightened for 1 minute. A frightened creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Second Roar. Each creature that fails a DC 18 Wisdom saving throw is deafened and frightened for 1 minute. A frightened creature is paralyzed and can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Third Roar. Each creature makes a DC 18 Constitution saving throw. On a failed save, a creature takes 44 (8d10) thunder damage and is knocked prone. On a successful save, the creature takes half as much damage and isn't knocked prone.

The sphinx can take 1 legendary action, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The sphinx regains spent legendary actions at the start of its turn.

Claw Attack. The sphinx makes one claw attack.