Flaming Hooves (Su): A blow from a nightmare’s hooves sets combustible materials alight.
Smoke (Su): During the excitement of battle, a nightmare snorts and neighs with rage. This snorting fills a 15-foot cone with a hot, sulfurous smoke that chokes and blinds opponents. Anyone in the cone must succeed on a DC 16 Fortitude save or take a –2 penalty on all attack and damage rolls until 1d6 minutes after leaving the cone. The cone lasts 1 round, and the nightmare uses it once as a free action during its turn each round. The save DC is Constitution-based.
Because of the smoke it gives off, a nightmare has concealment against creatures 5 feet away and total concealment against creatures 10 feet or farther away. The smoke does not obscure the nightmare’s vision at all.
Astral Projection and Etherealness (Su): These abilities function just like the spells of the same names (caster level 20th); a nightmare can use either at will.
How about a nightmare hit by one of its fired spines must make a save or lose access to its flight and plane-hopping powers for some duration (or until the spine is removed)?
I do, too.Ooh, I like that.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.