Fire Form: The elemental can fit into a place that is as narrow as 1 inch wide. If the target is a creature or a flammable object, it ignites. Until a creature takes an action to douse the fire, the target takes 3d10 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 ft..

 Water Susceptibility: For every 2 gallon of water splashed on it, it takes 1 cold damage.

Claw: Melee Weapon Attack: +3 to hit, reach 5 ft., one target. Hit: 2d6 + 3 fire damage. 

Bite: Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 2d6 + 5 fire damage. 

Fire Blast (Recharge 6): The Ancient Fire Cat opens its mouth, spewing fire in a 20 ft. cone dealing 3d8 fire damage.   The player must make a DC 14 dexterity saving throw.  If the target is a creature or a flammable object, it ignites. Until a creature takes an action to douse the fire, the target takes 2d10 fire damage at the start of each of its turns

The Ancient Fire Cat may use a legendary action out of three actions only in reaction to an attack on anybody.  It recharges at the end of the round. It has 3 Legendary Actions.

Pounce (Costs 1 Action): Jump in at most 30 ft. leap in any direction.  If it lands on a creature they are thrown 5 ft. in a random direction.  During Pounce, Ancient Fire Cat cannot be targeted by an attack of opportunity. 

Fire Wall (Costs 1 Action): The Ancient Fire Cat summons a large wall of fire in front of it to block one ranged attack from a wooden, nonmagical projectile.

Legendary Roar (Costs 2 Actions): The Ancient Fire Cat lets out a tremendous roar, giving  all allies 1d4 + its charisma modifier temporary health points.

Enter the description for how mythic actions work for your monster here.

Mythic Action Name (Costs # Actions). Enter the description for your mythic action.