After completing the first main island, Willma will ask for your help in saving both of her kids, Billdit and Maykit who went to separate places. Before making your choice, there will be a notification indicating this choice has more weight than you may think; here's how your choice affects the game.

I used to play Mario & Luigi RPGs on the Nintendo DS a long time ago. I always got a kick out of how they cleverly blended controls for both Mario and Luigi with button-mapping, making it feel like you were taking both on an adventure.