Illumination. The zombie sheds bright light in a 10 ft. radius and dim light for another 10 ft.  

Flyby.  The zombie doesn't provoke opportunity attacks when it flies out of an enemy's reach.  

Burning Body.  The zombie's melee attacks deal an extra (1d10) fire damage on a hit (included in the attack).  Additionally, when a creature touches the zombie or hits it with a melee attack while within 5 ft. of it takes 5 (1d10) fire damage.      

Innate Spellcasting. The zombie's spellcasting ability is Constitution (spell save DC 12, +4 to hit with spell attacks). It can innately cast the following spells, requiring no verbal or material components:

At will:  absorb elements*

3/day each:  burning hands, chromatic orb*

1/day each:  scorching ray, hellish rebuke 

*Fire damage only 

Cold Susceptibility.  If the zombie takes cold damage, it must succeed on a DC 15 Constitution saving throw, or any of its attacks, spells, or other effects that deal fire damage are halved until the end of its next turn.  If the saving throw fails by 5 or more, whenever the zombie makes an ability check, attack roll, or saving throw before the end of its next turn, the zombie must roll a d6 and subtract the result. 

For the same duration, the zombie can't use its Flame Combustion reaction.    

Slam. Melee Weapon Attack: +4 to hit, reach 5 ft., 1 target. Hit: 6 (1d8 + 2) bludgeoning damage, plus (1d10) fire damage.  The target must succeed on a DC 10 Dexterity saving throw or be set on fire.  While alight, a creature sheds bright light in a 5 ft. radius and dim light for an additional 5 ft.  The creature takes (1d6) fire damage at the start of its turns.  At the end of each of its turns, a burning creature can repeat the initial save, dousing the flames on a success.       

Hurl Flame. Ranged Weapon Attack: +4 to hit, range 30/120 ft., 1 target. Hit: 9 (2d6 + 2) fire damage.        

Flame Combustion (1/day).  In response to being damaged by a creature within 10 ft. of itself, the zombie bursts into flames.  Each creature within 10 ft. of the zombie must make a DC 12 Dexterity saving throw, taking (4d6) fire damage on a failed save, or half as much damage on a successful one.