Complex sentence: The Megablaster pilot will have to fend off the bizarre wildlife around them, but it is necessary to destroy the largest animals in each area as they have been fused with the bomb; once the creature is slain, the bomb is shut off.
Split into simpler sentences: The Megablaster pilot will have to fend off the bizarre wildlife around them. It is necessary to destroy the largest animal in each area as they have been fused with the bomb; once the creature is slain, the bomb is shut off.