Veteran Cathar

A green 2/2 that carries a white activation is an odd little machine, and the two-color split is exactly what governs how dangerous it gets. The body is plain beatdown; the to grant double strike is a deliberate tax, one that only fires when white sources sit in the manabase, which reserves the payoff for Selesnya Humans builds specifically. Because the ability targets any Human rather than only itself, it scales with a wide board: turn a single unblocked attacker into a real clock, or double the output of a pumped token late, when the green half of the deck has run out of relevant things to spend mana on. That gating keeps the design in check. A green creature that handed itself double strike for less, or entirely in its own color, would be a far more menacing card; pushing the activation into white and pricing it at four total mana ensures it matters only when both halves of the manabase are online and there is a board worth empowering. It sits among tribal commons that ask you to commit to a two-color identity before they pay out, and the reward here is a repeatable combat trick that lives on a creature instead of a card in hand, available every turn the mana is there rather than once from the graveyard or exile.