Arx

Immutable Form. The arx is immune to any spell or effect that would alter its form.

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

Spiky Hide. A creature that touches the arx or hits it with a melee attack while within 5 feet of it takes 4 (1d8) piercing damage. This trait also applies to the arx's walls.

Multiattack. The arx makes two Claw attacks and one Spear attack.

Claw. Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 18 (3d8 + 5) slashing damage.

Spear. Melee or Ranged Weapon Attack: +9 to hit, reach 5 ft. or range 20/60 ft., one target. Hit: 12 (2d6 + 5) piercing damage, or 14 (2d8 + 5) piercing damage if used with two hands to make a melee attack.

Wall Smash. If the arx has its wall set up (see Emplace Wall), it can briefly close the panels of the wall in on each other. Each creature other than the arx between the panels in a 10-foot cone from the corner where the panels meet must make a DC 16 Dexterity saving throw, taking 28 (8d6) bludgeoning damage on a failed save, or half as much damage on a successful one.

Emplace Wall (Recharge 3-6). The arx extends its hardened elytra and casts them into the ground, creating a wall. The wall is 3 inches thick and is composed of two 10-foot-by-10-foot panels. The panels must connect perpendicular to each other, forming a corner behind the arx. If the wall falls in a creature's space when the arx places it, the creature must make a DC 16 Dexterity saving throw. On a failure, the creature takes 10 (3d6) bludgeoning damage, and the arx determines to which side of the wall the creature is pushed. On a success, the creature takes half the damage and decides to which side of the wall it is pushed.