Well what's getting quite popular these days is the concept of a "loot box" which is where you spend some real money to get a box of unknown items. When you op

Well what's getting quite popular these days is the concept of a "loot box" which is where you spend some real money to get a box of unknown items. When you open it you get a randomised, by whatever factors, set of items/powerups/whatevers. It adds a bit of a gambling aspect to it where a user might want to pay again to have another roll of the dice. That's pretty easy to distinguish