Prophet of Kruphix

The descendant of Seedborn Muse with a creature-flash rider stapled on, and the combination is what makes it dangerous rather than either half alone. Seedborn Muse untaps your lands during every other player's untap step, which already converts a multiplayer table's worth of turns into open mana for you. Bolt the flash clause onto that and the untapped mana has somewhere to go: every opponent's turn becomes a window to deploy threats, blockers, and bounce-targets at instant speed, all funded by lands that refilled while everyone else was tapping out. The two abilities feed each other in a way that reads as a single engine, not a creature with two keywords. It also untaps your creatures during those steps, which turns vigilance into a non-issue and lets attackers double as defenders across the whole table. The 2/3 body is the honest part of the bargain: it dies to almost anything, and the whole apparatus folds the moment someone points removal at it, so protecting this five-mana enchantment-of-a-creature matters more than rebuilding it ever will. What distinguishes it from the older land-untappers is that green-blue framing: the flash clause is blue's contribution, the perpetual untap is green's, and the card sits exactly where those two colors' philosophies overlap on doing things when it isn't your turn.