Viceclaw

Spawn

 * Kill all the around the underwater rocks.  On clearing them, another ring of crabs will spawn.  If this ring is solo, kill them and wait for the respawn.  If this ring is heroic, on killing them either Viceclaw or a single solo con mudclaw crab will spawn once they go down.  If Viceclaw doesn't spawn, the only thing to do is kill the single crab and try again.