Complex statistics, maybe unlocked after you beat the game?
The game already tells you among other flags the amount of total human kills after every journey. I think it would be fun to have access to other statistics, such as number of times of transformations, the amount of items you've collected total, maybe causes of deaths or kills (who doesn't want to know how many enemies got BBQed?), stuff like that. It'd also be particularly useful for challenge runs so you could keep track of things like that. Maybe to keep things a surprise it could be an unlockable after beating the game?