These things are fairly weak, but they can be troublesome if too many come up. They tend to start coming in when the boss hits less than half health, and don't stop coming until the boss is dead (all Offspring out at that point automatically fall). A SMN 2 hour can wipe them all out in one swoop, and RNGs or BLMs can pick them off from afar to keep them off the melee. Just don't underestimate then.
Think of them as advanced versions of the Memory Receptacle's Strays.