Complex sentence: The Dom has anticipated their visit and, before Feric has the pleasure of killing him, triumphantly reveals that the Doms had succeeded in reactivating one of the ancient atomic weapons, a doomsday weapon, and he triggers the failsafe.
Split into simpler sentences: The Dom has anticipated their visit and, before Feric has the pleasure of killing him, triumphantly reveals that the Doms had salvaged and rearmed one of the ancient nuclear weapons. It is a doomsday weapon, and he triggers the failsafe.