Complex sentence: The First tells him that Brendan sold his soul in exchange for the biggest drink collection, but both agreed that the First must collect his soul at midnight the day he died or the deal will be null and void.
Split into simpler sentences: The First tells him that Brendan sold his soul in exchange for the biggest drink collection. But both agreed that the First must collect Brendan soul at midnight the day he died or the deal will be null and void.