Medusa, Inhuman Queen
Green as a spellslinger color is close to a contradiction, and this build leans into it by handing the payoff to a color that historically has none. The counter fires whenever any player casts a noncreature spell, not just its controller, which turns a personal engine into a table-wide clock. The timing is the part worth reading twice: the trigger keys on the cast itself, so growth banks before a spell ever resolves, though the trigger still uses the stack, so an opponent can respond by removing or bouncing Medusa before the counter is ever placed. That table-wide, cast-triggered growth puts it in the lineage of green's own accumulation creatures, Managorger Hydra and Forgotten Ancient among them, rather than the prowess creatures that only reward their own controller. It steers the deckbuilder away from green's usual creature-heavy shell toward cantrips, removal, and cheap noncreature permanents. Reach and vigilance signal how it means to close: swing every turn while holding a blocker back against the fliers a growing beater tends to attract. The catch is that green cannot supply its own noncreature density, so the second color in the pairing ends up doing more of the deckbuilding than the green in the cost. Left alone in a spell-heavy pod, the body accumulates counters on turns that are not even yours, and a modest creature can outsize the board well before it is ever relevant to attack.
