The fact that it gives any instant or sorcery spell you cast afterward Storm is also interesting and should lead to some good stories to tell later
If you dont cast the card, perhaps because you choose not to or because its a land card, it remains exiled
However, you must send all energies attached to it to your Lost Zone
Sometimes your Wizards will copy spells for you, while other times, they might return those spells from your graveyard back to your hand
In theory, with a Naban, Dean of Iteration on the battlefield, you only need half the number of blue mana symbols on the battlefield to make Master of Waves good (for example, in the worst-case scenario where you have just a Naban, Dean of Iteration and a Master of Waves, you'll still end up with 10 power across five bodies, which is a pretty reasonable deal for four mana, and if you throw just one other Wizard into the mix, things cat get out of hand really quickly when Master of Waves' enters-the-battlefield trigger is doubled)
If Mystic Confluence is copied, the effect that creates the copy will usually allow you to choose new targets, but you can't choose new modes
