Yesterday my players had their first encounter with them: 2 shards vs a party of 3 PCs, one NPC and their 5(!) dogs.
They were caught totally unprepared: the shards killed one of the PCs (the magician) on the spot with their first assault. The party then started to fight back, but in 2 rounds the monk lost a hand and teleported away to heal himself nad the NPC rogue died shortly thereafter. The dogs met a similar fate and either died or few from the battle (therefore proving themselves smarter than most of the PCs
).
In the end, the only PC still standing was the troll fighter: he managed to spot the shards, stun/entagle them with his bolas, then went berserk and beat them to a bloody pulp just before falling unconscious.