Ashen Nightmare

Siege Beast. The Ashen Nightmare deals double damage to objects and structures.

Stubborn. Ashen Nightmares are notoriously stubborn to anyone smaller than their size. Animal handling checks are made at disadvantage by creatures that are size large or smaller. 

Illumination. The nightmare sheds bright light in a 10-foot radius and dim light for an additional 10 feet.

Incendiary Aura. The fiery temper is overwhelming to those that end the round within 5 feet causing (2d4) fire damage.

Furnace Hide. A creature that touches the Ashen Nightmare or hits it with a melee attack while within 5 feet of it takes 2d8 fire damage.

Trailblazer. A fiery trail is left behind for the following round, as the Nightmare Steed passes, causing (1d4+4) fire damage to characters that pass through the trail or (2d4 + 4) fire damage to those that stand within the blaze.

Incorporeal Movement. The Ashen Nightmare can move through creatures and objects as if they were difficult terrain. It takes 5 (1d10) force damage if it ends its turn inside an object. While doing so, its body partially dissolves into burning smoke and drifting ash.

Smoke and Cinders. The Ashen Nightmare sheds choking smoke in a 15-foot radius while moving. Other creatures treat the area as heavily obscured. Moderate or stronger wind disperses the smoke until the start of the Nightmare’s next turn.

Multi-Attack. The Nightmare Steed can make 1 bite and 2 hoof attacks.

Bite. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 12 (2d4 + 7) bludgeoning damage plus 7 (2d6) fire damage.

Hooves. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 16 (2d8 + 7) bludgeoning damage plus 7 (2d6) fire damage.

Infernal Momentum. If the Ashen Nightmare moves at least 30 feet straight toward a target and hits it with a Hoof attack on the same turn, the target takes an additional 4d10 fire damage and must succeed on a DC 19 Strength saving throw or fall prone. If the target is Huge or smaller, the rider may immediately make one melee weapon attack against it as a reaction.

Flaming Rear (Recharge 5–6). The Ashen Nightmare rises onto its hind legs, screaming with infernal fury, before crashing its burning hooves into the ground. Each creature of the rider’s choice within 20 feet must make a DC 20 Dexterity saving throw. On a failed save, a creature takes: 3d10 bludgeoning damage + 3d10 fire damage and falls prone. On a successful save, the creature takes half damage and does not fall prone.

The ground in the area burns until the end of the Ashen Nightmare’s next turn. The area becomes difficult terrain, and creatures entering or starting their turn there take 2d6 fire damage.

Runes. Often the fire giants inscribe runes upon the saddle that the Ashen Nightmare can activate using a bonus action. The most common runes are inscribed using the Rune Shaper feat. 

Savage Bite.   Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 13 (2d4 + 7) bludgeoning damage plus 7 (2d6) fire damage.