Multiattack

The elder shadow drake makes one Bite attack and two Tail Slap attacks.

Bite

Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 17 (2d10 + 6) piercing damage.

Tail Slap

Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 15 (2d8 + 6) bludgeoning damage.

Invisibility

The drake magically turns invisible until it attacks, uses Shadow Step, or starts its turn in sunlight, or until its concentration ends (as if concentrating on a spell). Any equipment the drake wears or carries is invisible with it. The drake must be in dim light or darkness to use this action.

Stygian Breath (Recharge 5-6)

The elder shadow drake spits a ball of black liquid on a point the dragon can see within 60 feet of it. The ball bursts into a 20-foot-radius sphere of black mist centered on that point for 1 minute. Each creature in the mist when it appears must make a DC 15 Constitution saving throw, taking 42 (12d6) cold damage on a failed save, or half as much damage on a successful one. The mist spreads around corners, and its area is magical darkness. No natural light can illuminate the mist. If any of the mist overlaps with an area of light created by a spell of 1st level or lower, the spell creating the light is dispelled.