Because damage remains marked on a creature until the cleanup step or an effect removes that damage, nonlethal damage dealt to creatures you control may become lethal if Mirari's Wake leaves the battlefield.

The types of mana are white, blue, black, red, green, and colorless.

If tapping a land produces more than one type of mana, you choose one type that was produced and add one mana of that type.

If the mana produced by the land has any additional restrictions or riders, those restrictions or riders don't apply to the mana added by Mirari's Wake. You just get one mana of the appropriate type.