In the core rules of MegaMetroCity we can find two different play modes.
One shot mode. Players will be able to choose any stage and play in any difficulty level they choose. These levels are easy, normal, hard or very hard. In this mode, before the stage starts, the players will be able to acquire upgrades according to the difficulty level. At normal difficulty, for example, Heroes must get three upgrades.
History mode. Heroes will have to overcome each stage in order, trying to get at least one Hero to survive. In this play mode the difficulty of the next stage will depend on the number of upgrades the Heroes have acquired. The more upgrades you get during the stages, the higher the difficulty level.
Weapons, for example, lose some of their effectiveness as the difficulty goes up.