Asgea, Scholar of Worlds

At the beginning of your end step, if a spell or nonland ability other than Agea's added mana to your mana pool this turn, you get an experience counter.
At the beginning of your upkeep, you may add X mana to your mana pool in any combination of {w}, {u}, and/or {g}, where X is the number of experience counters you have. Until end of turn, this mana doesn't empty from your mana pool as steps and phases end.