Profit Hunt is a special type of mission in the game that allows you to battle Zombies for Marbles. To access this mode, open the Missions menu from the main game screen and select Profit Hunt.

In the newly opened window, you can see the available Zombie to attack, its strength, the rewards for defeating it, and the list of rewards for the collected marbles.

To attack the Zombie, tap the Challenge button at the bottom of the screen. You will need 1 Metro Key to initiate the attack.

After engaging in several battles against Zombies, you can either continue defeating stronger enemies to improve your rewards or claim the rewards for the Zombies you have already defeated.

When you collect enough Marbles of a certain type, you can claim the corresponding Baggage: