Sakura-Tribe Springcaller

The trick this engine plays is on the empty-pool rule, not on the cleanup step. Normally floating green from your upkeep evaporates the instant a phase or step ends, before you ever reach a spell worth casting; the clause here suspends that rule for the turn, so the upkeep green stays live through draw, main, combat, all of it, until end of turn empties the pool the way it always does. What you get is a green ritual paid on a recurring schedule rather than in one burst, one mana at the start of each of your turns, usable any time that turn but never carried into the next. The catch is that it never compounds: a single extra source of green each turn, no ramp spike. That makes it a strange middle creature between a mana dork that taps for immediate value and an enchantment that ticks a payoff up over a long game, doing the slow thing while a 2/4 body stands in front of attackers. The body is the part that earns the patience: four toughness is hard to trade with on the ground, which buys the early turns the engine needs to matter, and the same card that wants the game to go long is built to make getting there survivable. It rewards a deck with a curve that can spend one floating green per turn over many turns, not a deck hunting for one explosive ramp turn.