I'm with you guys.
For flavor, perhaps they are (slightly) redeemed vrocks of some sort?
The being speaks common and 2-3 other languages, as well as tongues exclusive to his mysterious plane.
A percentile roll of less than 50 minus the level of the caster indicates that the being tells a carefully fabricated and reasonably believable lie.
Its poison causes sleep for 1-6 days, during which time the being will eat its victim.
Its claws are infected with a terminal blood disease, as per the DMG.
The being has all the spell-like abilities of a type I demon, and it can travel in the Astral and Ethereal Planes.
Its other possessions number 2-12, each having a 20% chance of being magical in nature.
First off, we should drop the DR x/good from the vrock, as these aren't evil creatures. I could see replacing with /silver or /cold iron, though.
A being of the ball speaks Common, Abyssal, Celestial, Infernal and its own language?
That's a crazy-long duration for sleep. Knock it down to hours, or even minutes?
Demon fever seems a good fit (1d6 Con drain).
Astral projection and ethereal jaunt as SLAs, or borrow these?
Plane Shift (Sp): A spectral hound can travel from the Astral Plane to any plane that borders the Astral Plane and back again. This ability is similar to a plane shift spell, except that the spectral hound can transport itself only and it chooses its destination with pinpoint accuracy.
Ethereal Jaunt (Su): An ethereal marauder can shift from the Ethereal Plane to the Material Plane as a free action, and shift back again as a move action. The ability is otherwise identical with the ethereal jaunt spell (caster level 15th).
Treasure: Double items?
Could we make its DR something crystalline, to its harmed by a substance matching the ball that binds it?
That makes sense. Maybe throw in Draconic as well?
I'm OK with the long duration since they'll be woken up if the Being wounds them (although they would have to save vs sleep again if it uses its bite).
If we're going to cut it down I'd prefer hours.
Plane shift is my favourite among those suggestions.
The original owned a gem of seeing which is worth 75k in 3rd edition, that suggests a fairly good treasure.
I'm also thinking it's likely to collect gemstones.
How about Treasure: Triple goods (gems only), double items ?
Plane shift it is. Like so?
Plane Shift (Sp): A being of the ball can travel from the Astral Plane or Ethereal Plane to any plane that borders either and back again. This ability is similar to a plane shift spell, except that the being of the ball can transport itself only and it chooses its destination with pinpoint accuracy.

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