Whenever one or more Treefolk you control attack, add twice that much .
You don't lose unspent green mana as steps and phases end.
Build a wide, beefy board of Treefolk, swing in with vigilance so you keep blockers, and convert that attack into a flood of green mana that you don't lose as the turn progresses. Dump the surplus mana into giant X-spells, expensive bombs, or a finisher to close before opponents stabilize.
Generates explosive green mana from attacking that persists across all phases
Vigilance lets you attack and still hold the board defensively
Treefolk tend to be high-toughness, making them resilient to common board sweepers and combat
Mono-green struggles with interaction, removal, and answering noncreature threats
Mana payoff requires creatures on board and a profitable attack step
Slow, telegraphed gameplan vulnerable to fliers, evasion, and board wipes before you stabilize
Treefolk tribal is shallow, forcing reliance on generic green ramp and beaters