This skill is unlocked by completing a quest.
Usage:
groupcast ward breaker <wardstone>
This is an extremely old, extremely powerful spell that until recently had been lost to mortals. In a time of crisis, mortal champions rediscovered the spell and convinced one of the elder dragons to teach it.
The spell is used to break the keystones for certain types of wards. Once cast on a wardstone, the spell cuts off the internal flows of magic until an overload builds up and shatters the stone. Wardstones can be created with some protection against this, and sufficiently large wardstones may simply be able to absorb the overload without difficulty.
The spell also cannot be used on most smaller stones, as there simply isn't enough power in the wards to actually damage the stone.
This is not a spell of finesse or delicacy - it requires brute force to cast and operates via brute force. As such, large groups of mortals must typically pool their magic and cast it together.