Multiattack. The miner attacks twice with its hammer.

Hammer. Melee Weapon Attack: +6 to hit, reach 5 ft., 1 target. Hit: 8 (1d10 + 3) bludgeoning damage. 

Fire Breath. Ranged Spell Attack (recharge 5,6): range Self (30 ft line). Hit:  Each creature within range must make a Dexterity DC13 saving throw or take 21 (6d6) fire damage. You take half damage on a successful save.

Necrotic Flames. When the miner is damaged by an attack, they can use their reaction to send flames curling out of their mouth to attack the enemy that just hit them. The target must make a Dexterity DC13 saving throw or take 1d10 fire and 1d10 necrotic damage.