Siege Monster. The creature deals double damage to objects and structures.

Destruction Aura. All buildings rapidly deteriorate and crumble in Flamyr's Presence. Any humanoid-made structures within 30 miles of Flamyr are completely destroyed after 30 minutes.

Unstoppable. No material can slow or stop Flamyr.

Immutable Form. Flamyr is immune to any spell or effect that would alter its form.

Wish Resistance. The spell wish cannot kill Flamyr immediately. In such a case, Flamyr takes 20d10 Force damage and falls prone.

Spores. Flamyr can emit deadly spores. These spores plant in the ground after a use of the "Discharge Spores" action. Over the course of 6 months, these spores plant over a 30-mile area. This area becomes an unlivable wasteland inhabited by mutated creatures, shriekers, violet fungi, and other spore-based creatures.

World Ender (Mythic Trait). When Flamyr, The Jersey Devil is reduced to zero hit points, read aloud:

Flamyr lets out a soul-shaking howl, a mane of billowing jet-black hair emerging from its calloused, burned skin. It begins to get down on all fours, transforming into a hound-like beast. Two burning red eyes open on Flamyr's scalp, glaring at you. Flamyr mouth shifts to meet you, a menacing scowl present upon its face.

 After reading, Flamyr, The Jersey Devil transforms into Flamyr, The Howling Death.

Multiattack. Flamyr makes 2 claw attacks or 150 sting attacks.

Claw. Melee Weapon Attack: +30 to hit, reach 1000 ft., 10 targets. Hit: 75 (7d20 + 2) Slashing damage. 

Bite. Melee Weapon Attack: +30 to hit, reach 1000 ft., 10 targets. Hit: 50 (4d20 + 8) piercing damage, 50 (4d20 + 8) poison damage, and 50 (4d20 + 8) acid damage.  

Sting. Melee Weapon Attack: +30 to hit, reach 1000 ft., 5 targets. Hit: 1 (1d20 - 9) piercing damage. 

Lashing Tentacles. Melee Weapon Attack: +30 to hit, reach 1000 ft., 10 targets. Hit: 150 (14d20 + 3) bludgeoning damage.

Stomp (Recharge 4). Flamyr stomps. Each creature within a 666-mile sphere centered on Flamyr must make a DC 30 Dexterity saving throw, taking 150 (10d20) thunder damage on a failed save, or half as much damage on a successful one.

Breath (Recharge 5–6). Flamyr exhales in a 66-mile cone. Each creature in that area must make a DC 30 Dexterity saving throw, taking 63 (18d6) acid damage, 63 (18d6) fire damage, 63 (18d6) cold damage, 63 (18d6) force damage, 63 (18d6) lightning damage, 63 (18d6) necrotic damage, 63 (18d6) poison damage, 63 (18d6) psychic damage, 63 (18d6) radiance damage, 63 (18d6) thunder damage on a failed save, or half as much damage on a successful one.

Discharge Spores. All creatures within a 50 ft. sphere of Flamyr must make a DC30 Dexterity saving throw or take 150 (14d20+3) poison damage.

Rebuke. Flamyr uses this action after getting hit, but before damage is rolled. The creature takes 21 (2d20) Psychic damage.