My players finally faced the Ethereal Dragon I had take up residence in Stonehell's Lost Level. Thankfully they'd come prepared with a Dimensional Anchor spell that allowed all their attacks to hurt it!
Armor Class: 2
Hit Dice: 9+2** (M)
Move: 90' (30')
Attacks: 2 claws / Tail / 1 bite
Damage: 1d6+1 (claws & tail) / 3d6 (bite)
Breath Line: 75' x 5'
No. Appearing: 1 (1)
Save As: F10
Treasure Type: H
XP Value: 2,500
Monster Type: Dragon-kin (very rare)
Ethereal dragons are rarely encountered in the material planes, but when they are, they appear as white scaled serpents that gently glow. Their backs are ridged with short spikes, as are their legs and claws. Lacking wings, they're often not recognized as dragons, much to the woe of those encountering them. They are rarely speaking dragons, and somewhat lazy as few of the creatures they encounter can hurt them. When they come through to the material planes, they do it to hunt and steal. Because of their unique physiology, attacks on them from the material plane only have a 50% chance of actually causing any damage, unless made with a weapon designed to injure ethereal creatures.
The ethereal dragon's breath weapon is a line of oily rainbow light. While colorful, it will look wrong to anyone from the material planes. Anyone struck by the dragon's breath weapon will take the usual amount of damage (dragon's current hit points). Additionally the light is draining to creatures of the material realms, and will cause their Strength, Dex, and Con to be halved unless a saving throw is made. Lost ability points will be restored at a rate of 1/hour.