Skystreak Engineer

A 1/3 flyer that trades and blocks well early, then keeps a single upgrade in its back pocket for the turn it matters. Five mana, activated once ever, converts it into a 3/5 evasive threat; the once-only clause turns what would be a snowballing pump engine on a two-drop into a deliberate one-shot you cash in when a race or a stalled board rewards the bigger body. Leave it small to chump and trade in the opening turns, then commit the mana on your terms. Structurally this belongs with monstrosity and its kin: one-time investments that raise a creature's ceiling and then step aside, rather than level-up shells or repeatable engines that keep demanding to be fed. That capping is what separates the keyword from a genuine snowball; a repeatable +2/+2 for this cost would punish every tapped-out turn, while a single lifetime activation prices the upgrade as a decision, not an engine. The tradeoff is durability against permanence: the counters travel with the body, and they die with it. Death or a bounce spell erases the +2/+2, and no recursion recovers it, so the payoff is entirely front-loaded onto the specific creature you invested in. What the card sells is not raw efficiency but timing freedom within a strict budget: one big swing, taken exactly when you choose.