Fiery Body. A creature that touches the fire weird or hits it with a melee attack while within 5 feet of it takes 3 (1d6) fire damage. 

Flame Bound. The fire weird dies if it leaves the flames to which it is bound or if those flames are extinguished.

Invisible in Fire. The fire weird is invisible while fully surrounded by fire.

Flaming Lasso. Melee Weapon Attack: +5 to hit, reach 10 ft., one target. Hit: 12 (2d8 + 3) fire damage. If the target is Medium or smaller, it is grappled (escape DC 13). Until this grapple ends, the target is restrained and takes 5 (1d10) fire damage at the start of each of its turns, and the fire weird can't grapple another target.