Originally Posted by
Jowgen
A 720
The main limitations to using these crystals against hidden opponents are that a) you have to guess the square the creature is in, and b) only works if the creature is hidden thanks to concealment granted by a magical effect.
If the creature is hiding by means of invisibility, the lesser crystal would work, while other single-creature concealment providing effects would need the greater crystal. As the creature still has concealment after getting hit with the least crystal, it does not negate the hiding aspect.
If the creature is hidden by other means (e.g. hide in plain sight) then none of the crystals work to undo the hide.