Frantic Salvage

The instant-speed clause is the whole reason this exists. Plenty of effects recur artifacts from the graveyard, but most do it at sorcery speed or pull a single card to hand; this one batches an unlimited count back onto your library and replaces itself, all on the opponent's end step or in response to a sacrifice trigger. That timing is what turns it from a value spell into a buyback engine for artifact decks built around recursion: crack your fodder, hold up the four mana, and rebuild the top of your deck while a graveyard-hate spell is on the stack. The cantrip is what keeps it from feeling like a tempo-negative, since you replace the card you spent without losing a draw step. The "any number" is the part that scales, because it costs the same whether you reload one artifact or eight, which rewards a deck that floods its yard with cheap fixed costs rather than one expensive piece. It is a narrow card by construction: outside of artifact density, putting cards on top of your library is closer to a liability than an asset. But the design is honest about that narrowness, and within a graveyard-artifact shell the instant speed and the flat cost do real work that a hand-recursion spell at the same rate would not.