Molten Armor. Any creature that hits Gordoth with a melee attack takes 2d6 fire damage. Unyielding Fury. When reduced to 0 HP, Gordoth explodes in a wave of fel fire before dying. Each creature within 15 ft. must make a DC 16 Dexterity save or take 6d10 fire damage (half on success). Legendary Resistance (2/Day). If Gordoth fails a saving throw, he can choose to succeed instead.
Multiattack. Gordoth makes two Felblade attacks. Felblade. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 2d10+5 slashing plus 1d8 fire damage. Ground Slam (Recharge 5–6). Gordoth slams the ground, creating a shockwave in a 20-ft. radius. Each creature must succeed on a DC 16 Strength saving throw or take 4d8 bludgeoning damage and fall prone. Call Infernal Flame (1/Day). Gordoth summons a wave of fel fire in a 30-ft. line that is 5 feet wide. All creatures in the line must make a DC 16 Dexterity saving throw or take 8d6 fire damage and be ignited (take 2d6 fire at the end of their next turn).
Command Fire. A patch of fire within 30 ft. flares up. Any creature in that area takes 2d6 fire damage. Fel Step. Gordoth teleports up to 30 ft. to an unoccupied space he can see. Felblade Slash (Costs 2 Actions). Gordoth makes one Felblade attack.
On initiative count 20 (losing ties), Gordoth can take a lair action:
Dungeon, Cult Fortress, Molten Cavern