Aeras

Air Form. The Aeras can enter a hostile creature's space and stop there. It can move through a space as narrow as 1 inch wide without squeezing.

Multiattack. The Aeras makes two slam attacks.

Slam. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 14 (1d6 + 5) bludgeoning damage.

Dormant. The Aeras exists normally as a dormant crystal that appears translucent white. When another creature comes into direct contact with the crystal, the creature must make a DC15 Constitution Saving Throw. On a failure, the creature takes 3d6 Damage and the Aeras is activated with HP equal to twice the amount of damage dealt + 15. The Aeras occupies the same space as the creature when it is activated. On a successful save, the crystal is nullified, and is worth 500 gp. 

Whirlwind (Recharge 4–6). Each creature in the Aeras' space must make a DC 13 Strength saving throw. On a failure, a target takes 15 (3d8 + 2) bludgeoning damage and is flung up 20 feet away from the Aeras in a random direction and knocked prone. If a thrown target strikes an object, such as a wall or floor, the target takes 3 (1d6) bludgeoning damage for every 10 feet it was thrown. If the target is thrown at another creature, that creature must succeed on a DC 13 Dexterity saving throw or take the same damage and be knocked prone.

If the saving throw is successful, the target takes half the bludgeoning damage and isn't flung away or knocked prone.