If I was designing rules I'd make it that if two of the same C'Tan Shards are ever on the table at the same time, then they are both immediately removed from play and every unit on the board suffers D6 Mortal Wounds.
One Void Dragon Shard finds another Void Dragon Shard on the field of battle, and they both join as one and take vengeance on the Necrons who enslaved them before running off so they can't be recaptured.

















