SRD:Hoary Steed

HOARY STEED
A hoary steed’s natural weapons are treated as magic for the purpose of overcoming damage reduction.

Combat
Air Walk (Su): A hoary steed can ride through the air as well as on the ground, as though affected by a permanent air walk spell.

Astral Projection and Etherealness (Su): These abilities function just like the spells of the same names as cast by a 20th-level caster.

Magic Circle Against Good (Su): This ability continuously duplicates the effects of the spell. A hoary steed cannot suppress this ability.

Misty Breath (Su): The breath of a hoary steed functions like a constant obscuring mist spell.

Immunities (Ex): A hoary steed is immune to all charm and hold spells or abilities.

See Wikipedia Entry: Horse