One use only.
A model can use each of its Dark Shards once per game. Declare usage just before the model rolls to cast a non-Bound Spell. Any Dispelling Attempt made against this Casting Attempt suffers -D3 to the dispelling roll.
Roll this dice as soon as the Dark Shard is used. If a natural ‘1’ is rolled for this D3, the model using the Dark Shard suffers 1 hit with Toxic Attacks. This is an exception to the Casting and Dispelling Modifier rules (i.e. it is allowed to modify the dispelling roll by more than -2).