Conjurer's Bauble

The genius is that the cantrip almost never costs you anything. Bolting graveyard recursion onto a cheap, sacrificeable artifact that draws when cracked looks strange until you notice the recursion is incidental: the "up to one target card" clause lets you activate with no target at all, purely to send the artifact from the battlefield to the graveyard while still drawing. That second use is the engine. With a valid target you bury a single card from your graveyard onto the bottom of your library, then redraw, recycling a milled card or reloading a single key spell without overstuffing your hand. With no target you turn the sacrifice itself into a resource, feeding whatever cares about an artifact being put into a graveyard, all while drawing so the turn is never lost. What makes this work is that the act of sacrificing carries its own payoff, independent of the recursion stapled to it. Effects that return a card from the graveyard demand a target, which means they demand a graveyard worth digging into; this one makes the target optional and keeps the draw, so a hand with nothing to recur loses nothing. It grows a Tarmogoyf by adding a card type to the yard, triggers a sacrifice or graveyard-departure engine, recycles a spell back into the deck, and replaces itself, all for a single mana, and rarely forces you to choose which of those jobs it does on a given turn.