SD: Never surprised
It is never surprised because of the warning that its superb senses give the creature.
MR: 32%
When it is ready to attack, its wings beat together and thunder sounds.
This creature is never invoked. It always comes of its own will and does not leave until the battle is done.
It has been known to die in several battles against powerful beings, only to appear again years later to confront another evil.
Both, I think. It should also have good Spot and Listen.Shade said:Improved uncanny dodge and/or improved evasion?
Go with CR+8.What an odd number. That falls between CR+7 and CR+8. I'd lean toward the latter.
Was thinking the same thing myself.Some sort of deafening clap or other ability?
Sure. But maybe it should also have some way to know when nasty evil beings are summoned places, too.Some sort of "unsummonable" ability? Note that not even gates or epic spells can call it?
Yes.Rejuvenation/rebirth ability?

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