Matzalantli, the Great Door // The Core

The gating condition on the front side is what makes this a graveyard payoff disguised as a card-filtering engine. Three mana buys nothing exciting up front: tap to draw a card, then discard one, a looter that quietly stocks your yard with the permanent types the transform ability wants. The design logic is a slow build toward a threshold: four or more permanent types among your graveyard cards, at which point the four-mana activation flips the artifact into a land. Where the front side asks you to fill the graveyard, The Core cashes it in, tapping for a burst of any one color equal to the number of permanent cards you have buried. The two halves form a self-contained loop: the looter feeds the graveyard, the graveyard feeds the mana, and the count only grows as a game drags on. What separates this from other ramp is that it converts attrition into acceleration. Every creature that dies, every land that hits the yard, every spent artifact becomes fuel for a single explosive mana pop, the fathomless descent keyword doing exactly the counting work its name implies. The tension the card resolves is between card advantage and mana development: the same graveyard that the front side builds toward hand quality becomes, one transform later, a mana reserve that scales with how long you have been grinding.