Gwenna, Eyes of Gaea

Ramp that refuses to help anything but creatures, and that restriction is the whole engine. Two mana of any colors sounds like it should smooth out a control shell, but the spend clause locks it to creature spells and creature-source abilities, which turns a generic dork into a purpose-built accelerant for a specific kind of deck: one full of large bodies. The reward loop is where the design earns its name. Cast a creature with power five or greater and Gwenna grows and untaps, meaning a single fatty on turn four can produce another two mana toward the next fatty on the same turn. That untap is what separates this from a straight mana creature: it converts each big cast into fresh mana rather than just a one-shot ramp, so a curve of top-end threats snowballs into a chain instead of stalling after the first drop. Green has a long history of creatures that make mana for other creatures, but most of them are static taps that care nothing about what you spend the mana on; the power-five trigger is a builder's constraint, asking you to fill the deck with genuine haymakers rather than utility bodies, and rewarding you when you do with a mana engine that scales alongside the board it is helping to build.