Avatar of the Storm

Roiling Form. The elemental can enter a hostile creature's space and stop there. Space you occupy is considered difficult terrain and creatures within this space can only move at half movement. It can move through a space as narrow as 1 foot wide without squeezing but must use half it's movement to do so.

Empowered Attacks. Avatar of the Storm's roil slam attacks are treated as magical for the purpose of bypassing resistance and immunity to nonmagical attacks.

Multiattack. The elemental makes two attacks using any of combination of Roil Slam or Hurl Lightning.

Roil Slam. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: (8d8) force damage.

Hurl Lightning. Ranged Weapon Attack: +8 to hit, reach 100 ft., one target. Hit: (14d6) lightning damage and must roll a Constitution saving throw (DC 18) or become stunned until the start of their next turn. Flying creatures have disadvantage on this save.

Thunderclap (Recharge 6), reach 60-foot line. You bring your hands together in a booming clap; a booming wave of thunderous sound blasting out in a 60 ft line and 15 ft wide ahead of you. Each creature within this area must make a Dexterity saving throw (DC 18) or else take (20d6) thunder damage and (20d6) force damage, half on a success. On a failed save, creatures are pushed back 50 feet and are knocked prone, become stunned until the start of their next turn and are deafened permanently. On a success, creatures are pushed back 25 ft and are deafened for 1 minute. 

Razor Whirlwind (Recharge 6). Slicing winds batter creatures around you. Each creature within 5 ft of you and your space must make a Strength saving throw (DC 18). On a failure, a target takes (8d8) force and (8d8) slashing damage, and is flung up 30 feet away from the elemental in a random direction and knocked prone. If a thrown target strikes an object, such as a wall or floor, the target takes (3d6) bludgeoning damage for every 10 feet it was thrown. If the target is thrown at another creature, that creature must succeed on a Dexterity saving throw (DC 18) or take the same damage and be knocked prone. On a success, a creature takes half damage and is pushed back 15 ft.

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

Freezing Undertow (Recharge 6). You spread a foot high wave of water in a 50 foot cone and then pull the water toward you. Each creature within this cone make a Strength saving throw (DC 18). On a failed save, each creature within this wave is knocked prone and pulled 20 feet towards you. On a success, the creature remains standing but is pulled 10 feet instead.

A wave of cold then spreads on among the ice, freezing everyone inside solid dealing (8d6) cold damage. Prone creatures are considered grappled and restrained whilst standing creatures are considered grappled. Prone creatures can use their Action make a strength (Athletics) check at disadvantage (DC 18) to break out from the ice, whilst standing creatures can use their action to break free.