Steel Seraph

Cast it for and you have a 3/3 flier that reshapes an attacker every turn; cast it for the full and you have a 5/4 with identical text and a body that closes games faster. That gap is the whole point. Prototype hands the pilot two spells stapled to one card, and the choice isn't between different abilities (those never change) but between when the mana is worth spending. Flooded on lands, the Seraph is a finisher you didn't have to draw separately. Short on mana, the small mode is a curve-appropriate flier that still shapes combat. The combat trigger is the connective tissue across both modes: at the start of your combat it hands a creature you control flying, vigilance, or lifelink, so the Seraph can fly in for damage while lending evasion to a ground threat, or feed itself vigilance and swing while staying home on defense. That last option matters because flying is all the card brings natively; vigilance and lifelink exist only as the trigger's gift, which is what keeps the effect scarce rather than free. The keyword was built to soften the mana-screwed and mana-flooded extremes that decide too many games, and a repeatable, redirectable combat buff bolted to a scalable flier is about as clean a demonstration of that design goal as Prototype produced.