Rooftop Assassin

The removal clause is a payment plan, not a coupon. Flash and flying make the body a legitimate ambusher, able to block a flyer and survive to trade or tag it later, but the enters-the-battlefield kill only fires on a creature an opponent controls that already took damage this turn. That splits the card into a two-part sequence: put a point of damage on something first (a creature you blocked, a creature that ran into a blocker of yours, a burn spell that chipped it down), then flash this in as the follow-through that finishes what the damage started. Lifelink stitches the halves together, because the combat where you set up the kill is usually a combat where you are taking damage too, and clawing that life back matters. This is a conditional Murder bolted onto an evasive lifelinker, and the softening requirement is where the balance lives: unrestricted flash removal on a flying body would be oppressive, so the destruction is priced behind work you have to do yourself. What lifts it past a value creature is the tempo shape of that setup. It rewards leaving black mana untapped through combat and punishing an opponent who commits creatures into it, the kind of instant-speed pressure a sorcery-speed removal spell never applies. The prerequisite is real, but so is the reach of a kill spell you can hold for the exact moment the damage lands.