Angelic Favor

Tap a creature you weren't going to use anyway, and for that single cost you ambush the combat step with a 4/4 flier that evaporates before the turn ends. The printed mana line is a fiction for most white decks: as long as you control a Plains, this spell wants its alternative price, which is to bow exactly one untapped creature rather than four mana. Because the Angel enters without haste and is exiled at the beginning of the next end step, it can never be declared as an attacker; it exists for one purpose, to block, and the combat-only clause pins the whole effect to the one phase where a surprise body changes the damage math. That makes it a near-free flash defender on a board already committed to combat, a way to eat an attacker or trade up at instant speed without spending mana. The exile rider is doing the balancing: the token lives for a single combat, so the card never compounds the way a token engine would and never leaves a permanent threat behind. The design predates convoke's formal keyword while circling the same idea from a narrower angle, since the tap is not "tap any number of creatures" but "tap precisely one." Read off its cost it looks like an overpriced instant; played correctly it is a free ambush blocker, with the Plains requirement and the single-creature tap keeping that rate in check.