Ur-Golem's Eye

Mana rocks live or die on whether they ramp into something the colored-mana version can't reach, and this one was built for the cast where the payoff only speaks colorless. Four mana that taps for two is a net loss in raw acceleration: it costs more than it returns until you've untapped with it twice. The point was never speed. It was feeding the hunger of artifact-heavy decks where the symbol itself is the constraint, the kind of board where Tron lands answer the same question this does, just faster. Where it earns its slot is the count: a rock that produces two of one specific resource lets a deck hit colorless thresholds (big artifact creatures, activated abilities priced in generic mana, payoffs that demand pure ) without diluting the manabase across colors. It is invisible to most decks and decisive in the few that care, which is exactly the profile that keeps a four-mana two-rock relevant long after cheaper, more flexible accelerants would have buried it. Most colorless ramp printed since has either come down sooner, attached a condition, or ridden on a creature; this one stays pure, leaving your colored sources untouched while it hands back a resource only the most starved artifact shells have learned to spend.