Balrog

Fire Form.  A creature that touches the balrog or hits it with a melee attack while within 5 feet of it takes 5 (1d10) fire damage. The first time it enters a creature's space on a turn, that creature takes 5 (1d10) fire damage and catches fire; until someone takes an action to douse the fire, the creature takes 5 (1d10) fire damage at the start of each of its turns.

Illumination. The elemental sheds bright light in a 30-foot radius and dim light in an additional 30 feet.

Water Susceptibility. For every 5 feet the elemental moves in water, or for every gallon of water splashed on it, it takes 1 cold damage.

Multiattack: The balrog makes 1 burning whip attacks and 2 burning sword attacks.

Burning whip:  melee, +9 to hit, 30ft range, 1d10 fire damage+ 1d6 slashing damage. The target creature must make a strength saving throw vs the Balrog or be restrained and pulled 30 ft towards the Balrog. For each turn the creature spends restrained it must make a constitution saving throw or take 1d10 fire damage.

Burning Sword: melee, +10 to hit, 10 ft range, 1d12 fire damage+ 1d8 slashing damage. When a creature is pulled towards the Balrog it can make an attack of opportunity with it's burning sword against the target.