Another weird troll offshoot!
Crystalline trolls have 10 giant RHD, ability scores that are a bit less impressive than the cave troll's, mental stats that are low, but not abysmal, weak (1d6) claws and bite, acid immunity, and a moderate rend ability.
Most notably, they have regeneration 5 that's overcome only by sonic damage (which they are also vulnerable to). That's pretty huge: while fire and acid aren't the most uncommon damage types, sonic is found on only a handful of monsters.
Note that this doesn't mean most foes can't kill you: if all else fails piling dirt on your face and smacking you for a few minutes lets them execute you. It does, however, mean that during combat almost no foes can permanently keep a crystalline troll down, and that barring a TPK, combat is almost never truly dangerous.
That said, no matter how nice the regeneration is, ultimately I don't feel like the crystalline troll's offensive presence is sufficient to do it justice. -0 LA for now, but open to suggestions for +0.