Archsphinx

Fortitude. If damage reduces the sphinx to 0 hit points, it must make a DC 30 Constitution saving throw, unless the damage is from a critical hit. On a success, the sphinx drops to 1 hit point instead.

Imprisonment (2/Day). The Sphinx can cast the imprisonment spell, requiring no material components and using Wisdom as the spellcasting ability (Save DC 23).

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 its intentions or sincerity have disadvantage.

Legendary Resistance (3/Day). If the Sphinx fails a saving throw, it can choose to succeed instead.

Magic Resistance. The sphinx has advantage on saving throws against spells and other magical effects.

Unusual Nature. A sphinx does not need food or sleep.

Multiattack. The Sphinx makes two claw attacks; or it makes one claw attack and casts a spell with a casting time of 1 action.

Claw. Melee Weapon Attack: +12 to hit, reach 5 ft., one target. Hit: 21 (3d10 + 5) slashing damage. If the target is a creature, it must succeed on a DC 23 Wisdom saving throw or take 14 (4d6) psychic damage after each attack it makes against the Sphinx before the start of the sphinx’s next turn.

Sacred Flame (Cantrip). Flame-like radiance descends on one creature the sphinx can see within 60 feet of it. The target must succeed on a DC 23 Dexterity saving throw or take 18 (4d8) radiant damage, gaining no benefit from cover.

Supreme Authority. The sphinx chooses up to three creatures it can see within 90 feet of it. Each target must succeed on a DC 23 Intelligence saving throw or the sphinx chooses an action for that target: Attack, [Tooltip Not Found], Dash, Disengage, Dodge, Help, Hide, Ready, Search, or [Tooltip Not Found]. The affected target can’t take that action for 1 minute. At the end of each of the target’s turns, it can end the effect on itself with a successful DC 23 Intelligence saving throw. A target that succeeds on the saving throw becomes immune to the sphinx’s Supreme Authority for 24 hours.

Spellcasting. The sphinx casts one of the following spells, requiring no material components and using Wisdom as the spellcasting ability (spell save DC 23, +14 to hit with spell attacks):

at will: guidance, mage hand, prestidigitation, thaumaturgy

1/day each: antimagic field, word of recall, scrying, dispel evil and good, divination (as 1 action), locate creature, blight, tongues, dispel magic, arcane lock, hold person, silence, sanctuary, scrying (as 1 action), silence, command, detect evil and good, detect magic, unseen servant

Spellcasting (1/Day). The sphinx can innately cast divine word (spell save DC 23). Its spellcasting ability is Wisdom.

Counterspell (3rd-level Spell; 1/Day). The sphinx attempts to interrupt a creature that it can see within 60 feet in the process of casting a spell. If the creature is casting a spell of 3rd level or lower, its spell fails and has no effect. If it is casting a spell of 4th level or higher, the sphinx makes a Wisdom check with a DC equal to 10 + the spell’s level. On a success, the creature’s spell fails and has no effect.

The sphinx can take 3 legendary actions, 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.

Attack. The sphinx makes one attack.

Cast a Spell (Costs 2 Actions). The sphinx casts a spell of 3rd level or lower from her list of prepared spells. This counts as one of its daily uses of the spell.

Supreme Authority (Costs 3 Actions). The sphinx uses Supreme Authority.