Void Form. The elemental can enter a hostile creature's space and stop there. The elemental can fit through any gap without squeezing. 

Invisible. The elemental is invisible.

Vacuum Aura. The elemental continually sucks the air out from the area around it. All breathing creatures within 5 feet of the elemental must be holding their breath or else they will suffocate.

Multiattack. The elemental makes two slam attacks. 

Slam. Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit:  9 (1d8 + 5) bludgeoning damage. The target must make a DC 15 Constitution saving throw. On a failure, the creature's Constitution score is reduced by 1d4 points. The target dies if this reduces its Constitution to 0. Creatures made of air or gas have disadvantage on the saving throw, and creatures that do not need to breath automatically succeed  

Steal Breath (Recharge 6). Each creature in the elemental's space must make a DC 15 Constitution saving throw. On a failure, a target takes 28 (5d8 + 2) bludgeoning damage and is suffocating, and their Constitution score is reduced by 1d4 points. The target dies if this reduces its Constitution to 0. A suffocating creature that fails the saving throw drops to 0 hit points and is dying. On a successful save the creature takes half damage, is not suffocating, and does not suffer the Constitution score reduction. Creatures made of air or gas have disadvantage on the saving throw, and creatures that do not need to breath automatically succeed.