Complex sentence: The plan backfired, as Annar's creations proved to be mindlessly hostile and capable of asexual reproduction; unnable to contain the monsters, the crew of the Prometheus was slaughtered.
Split into simpler sentences: The plan backfired, as Annar's creations proved to be mindlessly hostile and capable of asexual reproduction. Unable to contain the monsters, the crew of the Prometheus was slaughtered.