I've been farming these things for over an hour - not a single drop of Crushed Shards...I have all the other keys and they spawn no problem. Just sitting around here farming. I think it might be a lost cause 
public override void OnDeath( Container c )
{
base.OnDeath( c );
if ( Utility.RandomDouble() < 0.05 )
c.DropItem( new CrushedCrystals() );
if ( Utility.RandomDouble() < 0.1 )
c.DropItem( new IcyHeart() );
if ( Utility.RandomDouble() < 0.1 )
c.DropItem( new LuckyDagger() );
}