Kayla's Music Box

The split between its two abilities is the whole design. The first banks cards one at a time, paying a white mana and a tap to exile the top of your library face down; the second unlocks the entire hoard at once, tapping to let you play everything stored under the box for a single turn. Because the exile is face down but the reminder text lets you peek any time, this is not blind card advantage the way most impulse effects are: you know exactly what you have squirreled away, so you can pace when to spend a whole turn cashing out. The tension is timing. Every card you bank costs a full activation and a mana, and nothing you exile does anything until you spend a separate tap to open the vault, so the artifact rewards a plan that fronts the setup and then converts a stockpile in one burst rather than dribbling value out card by card. It is a value engine built around delayed gratification, asking you to think several turns ahead about how much you can afford to lock away before the turn you finally break it open. The face-down peek is the quiet piece that makes the whole thing work: you are never guessing at what you have stored, only choosing the moment to release it.