Pool table? Mars' nen ability should be a dead giveaway that he's stupidly good at games like marbles and pool. 
Mars: (/^_^)/ "Ivy~, wanna play a game~? If I win, you have to leave your door unlocked tonight~<3. If you win, you get to punish me in any way you want~. It'll be fun!"

And how long is the actual trip to the dark continent going to be? Fun things tend to happen with characters are stuck together in a confined space for any amount of time.