Vasuthants are D&D's answer to the question 'what if black holes were undead'. The answer: a pretty neat little 2 RHD, Small-sized monster.
The shadowblobs have surprisingly okay stats, with no constitution, 10 strength, 16 dexterity, 14 charisma, 12 wisdom and 4 intelligence. The last of those hurts, but it's still a net +6. They move at a perfect 30 ft. fly speed, which is pretty nice.
Defensively, vasuthants enjoy immunity to acid and cold, resistance to fire and electricity, +2 turn resistance, Unholy Toughness, and immunity to every single spell that has the Light descriptor or is from the Sun domain (which sadly seems to be mostly subpar blasting).
They are also surrounded by an aura of shadows (penetrated normally by low-light vision), which has mixed effects. Miss chances are always good, but in D&D virtually anything has low-light vision by virtue of its type (the only exceptions are some aberrations and a handful of humanoids). In fact, I wouldn't be surprised if in most encounters the only being meaningfully affected by the aura is the party's token human. Rendering the party incapable of using light sources doesn't help a lot either.
Another of note is Reality Distortion, which is actually pretty good. It lets the vasuthant reroll any one die (whether it's for its own action, an opponent's, or an ally's) thrice a day, which definitely has its uses in letting allies survive save-or-dies and letting your casters' hit theirs. The limited number of uses is sadly a problem.
Interestingly, vasuthants seem to be designed with grappling in mind: they get Improved Grapple for free, have Improved Grab, and have a special ability (Enervating Crush) that allows them to drain strength from grappled creatures. The issue with the latter ability (and their apparent goal as grapplers in general): vasuthants are Small, with no strength bonus and medium-BAB RHD. A by-the-book ECL 2 vasuthant is grappling about as well as the party's human wizard: one with significant strength investment will be comparable to a 16 strength martial. This would be bad enough on its own, but Enervating Crush does not work on larger creatures. Given that the number Small enemies tends to drop off significantly after the obligatory Level 1 Goblin Dungeon, this ability might as well not exist for the bigger part of a vasuthant's lifespan.
Some might wonder whether RHD-advancement can help out here, as it did for some monsters in the past, but no. Vasuthants don't reach Medium size until 6 RHD, and don't reach Large size until 10 RHD. A 6 RHD vasuthant with maximum strength investment may have 23 strength and Improved Grab, but it's also behind three points of BAB (and an iterative) compared to martials, and still can't use Enervating Crush against the many Large opponents that started popping up a few levels ago.
The vasuthant is a cool concept, but in practice it'll just be a hard-to-kill party-blinding slotless blob, whose feeble attempts at grappling will fail against most foes and don't do much even if they succeed. The 3/day rerolls are nice, but insufficient to justify two less-than-great hit dice. I guess you could be a warlock and just try to kite stuff to death: but early-game flight is accessible with less opportunity cost. -0 LA: my hopes for this one are dashed.
I like to kid about 'greater' versions of a monster just being the same thing with twice the RHD, but the horrific vasuthant takes the cake. It's got not twice, not thrice, but twelve-and-a-half times the RHD of its lesser cousin.
Granted, it gets a lot of upped numbers and even some new abilities, but not enough to justify playing five levels into epic. If we judge this as a caster, it has to compete with Epic spells. If we judge this as a martial character, it's still only got 12 BAB and numbers that, while big, don't do a lot against the average enemy at this level. -0 LA.