Complex sentence: Was killed when attempting to crash the Moon into the Earth and Zelretch sneak attacked him, as the Crimson Moon never bothered to learn Magic which is the realisation of miracles, he was taken by surprise and killed.
Split into simpler sentences: Was killed when attempting to crash the Moon into the Earth and Zelretch sneak attacked him. As the Crimson Moon never bothered to learn Magic, which is the realisation of miracles, he was taken by surprise and killed.