Twinferno

Neither mode on this modal instant answers something already resolving on the board; both are bets placed on what comes next. Pick the copy line and you arm a delayed trigger: your next instant or sorcery this turn gets duplicated, with the copy free to point wherever you like. Nothing happens until that follow-up spell lands, so your two mana buys nothing on its own; it presumes a second card worth echoing is already in hand. A burn spell doubles into lethal, an X-effect swells, a tutor or draw fetches twice over; the copy simply inherits whatever ceiling the mirrored spell was already carrying. Pick double strike instead and you get red's plainest combat closer, a turn's worth of first-strike-plus-regular damage granted to a creature you're already fielding. The friction in this design is that the two modes want opposite shells. The copy line rewards a spell-dense build that feeds on its own stack; double strike wants a board and something to swing with, and cares nothing for what else you're holding. Most modal cards give two roads to the same outcome. This one hands a single answer to each of two decks that would rarely be built together, and it assumes the caster made that choice long before the card was ever drawn.