Sunstrike Legionnaire

A tapper that resets itself off your own board's churn: instead of untapping on schedule, it comes back online every time another creature lands on the battlefield. That single rewrite of the untap rule is the whole hinge. A conventional tapper holds down one threat per turn cycle; this one can lock the board if your creatures keep entering, because each new arrival hands the Legionnaire another activation that turn. The mana value 3 or less clause on the tap target is the price for that machine-gun potential, scoping it to early drops and most utility creatures while keeping it off the genuinely large finishers it would otherwise neutralize for free. The result is a card that wants to sit in a deck pumping out small bodies, where it converts a wide, cheap battlefield into a soft prison on the opponent's defenders or attackers. Pulled out of that context it does little: with no creatures entering, it taps once and then sits exhausted indefinitely, a 1/2 that has forgotten how to untap. The design tension is honest. The reward scales with how busy your board is, and the cost is total dependence on that traffic.