The Celestus

Left to their own devices, day and night flip according to a spell-count rhythm neither player fully controls: a diffuse, semi-passive clock that no single card owns. This artifact seizes the clock. For three mana and a tap, at sorcery speed, it lets you drive the cycle on your terms rather than waiting for the board state to nudge it. The clever part is where the payoff sits: the trigger keys off the transition, not the state, so churning the cycle in either direction gains a life and lets you loot (draw, then discard). That means it rewards motion, not squatting on a favorable side. The flip is gated by the tap symbol rather than a per-turn cap, so untap effects can chain it several times in one turn, though each pass still costs three mana, which is what stops a repeatable draw-and-discard engine from arriving free. It also cleans up the awkward edge case in the mechanic's own rules: outside a game that has entered the day/night system there is neither day nor night, and this simply declares day as it arrives, then hands you the button to move things from there. A colorless source that fixes any color, keeps the graveyard fed, and drips life while it does so: an artifact that both starts the machine and runs it.