Complex sentence: He also managed to render the base's defense systems completely inoperative by inserting bombs here and there, opening the door for a Destron attack, but when the Headmaster Juniors were almost killed in the following fight, Clouder regretted his actions and disappeared without a trace.
Split into simpler sentences: He also managed to render the base's defense systems completely inoperative by inserting bombs here and there, opening the door for a Destron attack. But when the HeadMaster Jrs were almost killed in the following fight, Clouder regretted his actions and disappeared without a trace.