Complex sentence: Mario, Luigi, Peach and Toadsworth decided to head back to the Mushroom Kingdom after a long journey but before they can leave, Peasley brought a farewell gift for them to take home, which was Bowser, who regained memory.
Split into simpler sentences: Mario, Luigi, Peach and Toadsworth decide to head back to the Mushroom Kingdom after a long journey. Before they can leave, Peasley brings a farewell gift for them to take home, which is Bowser, who regained memory.