I know, right?
So, each stat has a minimum, usually 35 or above, and then several D10s, the exact amount depending on the stat, are rolled. For reference, the minimum strength and toughness are 49, and the max is 85, as they start at 45 and you roll 4D10 to add to it. From there, they have all manner of terrible traits and talents, a couple being a This or This, Rogue Trader style selection (Assassin Strike or Hatred (All) is one instance).
C'Tan Shards ignore cover when attacking - period, their natural attack has 10 pen and raises the overload on a field they hit by 10, they have a natural forcefield (45 with no overload), are immune to any and all environmental effects (Black holes and super novas are among the examples) and get 2 or 3 abilities off of a table you roll on. The abilities are crazy things like causing an extra mission complication and forcing characters to make Perception tests or count as blind and deafened, or things like the area around them counting as a high gravity environment, or darkness that no tool can see through.
High-rolled C'Tan Shards could definitely stand their ground against Greater Demons. They're pretty cool. There is a lot to them, and you can make one Shard a COMPLETELY different combat experience from another. FFG did a great job with them.