Great Oak Guardian

Flash on a green creature is rare enough that this 4/5 pins its whole case to the surprise: a combat ambush a defender cannot see coming. The enters trigger reads like a Falter run in reverse, pumping a player's whole board and untapping it instead of stripping blockers away, and the cleanest line is the defensive one. Hold it up on an opponent's turn, then cast it after their attackers are declared but before blocks lock: the untap frees your tapped-down creatures to throw into the swing, and the +2/+2 reshapes every block they were counting on. On your own turn it is straight offense, where the untap matters less (your team refreshes at your next untap step anyway) and the buff does the closing work. The targeting clause cuts both ways, since the +2/+2 and untap hit a player's creatures: a personal trump on your turn, a political favor you can hand an ally elsewhere. Reach is the quiet justification for keeping it raised against fliers when no combat develops. Six mana is a steep tag for a single instant-speed effect bolted to a midsize body, and the honest counterweight is that you pay for permanence: the trick arrives as a creature that stays. That puts it out of reach of Negate-style counters that name only noncreature spells, though it remains vulnerable while resolving to a creature-permitting counter, or to discard before you ever get to cast it.