Ancient Defender

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

False Appearance. While the defender remains dormant, it is indistinguishable from the sand around it.

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

Sandstorm. As an action, the defender can summon a sandstorm. Any creature within 60 ft. of the defender has their visibility reduced to 10 ft. and any creature within 15 ft. of the defender is blinded. This effect lasts for 1 minute or until the defender loses consciousness.

Desert Coffin. As an action, the defender can solidify the sand around a single creature. The target must make a DC 16 Dexterity saving throw or be paralyzed. While paralyzed in this way, at the beginning of each of its turns, the target takes 21 (6d6) bludgeoning damage. The target can use its action to attempt to break free with a DC 16 Athletics check.

Multiattack. The defender makes either two slam attacks or one slam and one boulder attack.

Slam. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 16 (2d12 + 3) bludgeoning damage. 

Boulder. Ranged Weapon Attack: +3 to hit, range 10/40 ft., one target. Hit: 25 (4d10 + 3) bludgeoning damage.

Shifting Sands. When the defender is hit with a melee attack, it can use its reaction to gain resistance from that attack.