Throne of Geth

Proliferate's first repeatable engine piece, and the one that turned the keyword from a one-shot rider into something you could build an entire deck around. A single proliferate trigger, the kind stapled onto a sorcery or a creature's enters-the-battlefield ability, fires once and is gone. This converts the act of sacrificing an artifact into a proliferate on demand, every turn, for as long as you have fodder. That reframes what the keyword is good for: instead of nudging a planeswalker one tick closer to ultimate, it lets you grind charge counters, +1/+1 counters, poison, level counters, and oil up in a sustained loop. The sacrifice clause is what pays for the repeatability; it asks you to bring a supply of expendable artifacts rather than handing you a free spigot, and in an artifact-dense shell that cost is barely a cost at all. The activation is a tap ability, so it sits at instant speed and can wait until end of turn or respond to your opponent's actions. What it represents is the moment proliferate stopped being a keyword you triggered and became a keyword you operated, the difference between a mechanic that appears in your deck and a mechanic your deck is built to abuse.