Paraelemental.The smoke elemental can be in a semisolid state made of swirling hot ash and soot forming itself into any large shape it wishes or a formless smoke. It can use its action to change between the two forms.

While in smoke form, the elemental can’t speak, manipulate objects or take any actions besides its smother attack and split bonus action. It is weightless, has a flying speed of 20 feet, can hover, and can enter a hostile creature’s space and stop there. A creature in the smoke elementals space is considered blinded. In addition, if air can pass through a space, the smoke can do so without squeezing, and it can’t pass through water. It has advantage on Strength, Dexterity, and Constitution saving throws

Multiattack. The elemental makes two slam attacks or one smother attack

Slam. (semisolid form only) Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 9 (1d8 + 5) bludgeoning damage. plus an additional: 4 (1d8) fire damage.

Smother.(smoke form only) Melee Weapon Attack: +8 to hit, one target in the smoke elementals space. Hit: 11 (2d6 + 5) fire damage as the smoke elemental enters the creatures lungs attaching itself to the target. At the start of the creatures next turn it can make a DC15 Constitution Saving throw on a success the Smoke elemental is ejected from the creatures space and is unattached, on a failure the creature takes another 2d6 fire damage and begins suffocating - creatures who do not need to breath do no begin suffocating.  The creature can repeat the saving throw at the start of each of its turns, ejecting the elemental from its space on a success or taking 2d6 fire damage on a failure. The smoke elemental can only smother one creature at a time. A powerful gust of wind such as from a gust of wind spell or cold damage forces the elemental to detach from a target it's othering ejecting it from the creatures space. 

Split. (smoke form only) if the elemental has more than half it's total hit points it can split into 4 tiny smoke elementals each with a quarter of its current hit points rounded down, they have a +2 to attack rolls and deal 1d4 fire damage for its smother attack, and it can no longer change into a semisolid state, otherwise its statistics remain the same.