Complex sentence: Yusei and Jaden arrive and take Yugi to half an hour before Paradox's attack, deducing that by killing Pegasus, Paradox would be able to end the existence of Duel Monsters, which would radically change the course of history.
Split into simpler sentences: Yusei and Jaden arrive and take Yugi to 30 minutes before Paradox's attack. If Pegasaus dies too early, the existence of Duel Monsters would end, which would radically change the course of history.