Shang-Chi, Martial Mentor

Green has doubled +1/+1 counters before, from Doubling Season on down, but those doublers arrive as an enchantment or a passive body and rely on other cards to supply the counters they multiply. This design folds the doubler onto a creature that also seeds itself. The static clause converts every +1/+1 counter your creatures would receive into two, so any +1/+1 counter source you play runs at double rate the moment the body resolves. Then the power-up line hands it a one-time jumpstart: pay the cost to put three counters on it, which the static effect promptly turns into six, a self-contained payoff that needs no support piece to threaten. That pairing is the interesting part. A doubling effect is only as valuable as the counters it doubles, and most such effects sit dead until an enabler shows up; bundling even a single burst of counters onto the same permanent means the card justifies itself the turn it lands rather than waiting. Because the power-up can be activated only once, it functions as a built-in floor rather than an engine: one guaranteed six-counter swing regardless of the board, with a counters-matter shell scaling far past that. The reduced cost for having entered the same turn is the tell about intent, cutting the price when you deploy and immediately commit, tightening the window between resolving the creature and turning it into a finisher instead of a slow value piece.