Battlefly Swarm

The whole design lives in a single decision an opponent has to make about the air. Flying already narrows the field of legal blockers to other flyers and reach creatures, so the black activation is aimed at exactly that thin slice of the sky: hold up a mana, and any bigger flyer that commits to a block trades away for a 1/1 that dies making the exchange. That is the honest frame, not a repeatable engine but a threat that reprices every block the opponent might declare. Because the body has no first strike, granting deathtouch buys a one-for-one at best, so the card's real leverage is the untapped mana sitting behind it before combat rather than the trade itself. The activation draws on the same black source the rest of the deck wants, which is what keeps it in check: each turn asks whether a point of evasive damage is worth more than the deathtouch insurance, and the insect is only as dangerous as the mana held open. The decision is concrete and made at the moment a block is declared, not an abstraction. A small, disciplined threat whose whole value is the doubt it plants: whether it is safe to block, and whether it is safe to tap out into it.