Act of Heroism

The untap clause is what separates this from a stock combat trick. A +2/+2 for two mana would be unremarkable; untapping the creature first turns the card into a defensive ambush tool, and the timing window is everything. Because the +2/+2 and the extra block both fade at end of turn, casting it on your own turn after combat is wasted: the creature untaps, then the boost evaporates before the opponent ever swings. The card wants to be held up on the opponent's turn instead. Let them attack into open white mana, then untap a tapped creature, grow it +2/+2, and let it eat an attacker it should never have been able to block. The additional-block grant compounds the trap: one enlarged, untapped blocker can soak two attackers at once, so an opponent who committed to a multi-creature swing watches their math come apart in a single instant. (Worth noting what the extra block does not do: a creature that can block an additional creature still cannot block something with menace, which always demands two separate blockers.) It works on offense too, pushing a tapped creature through a block it would otherwise lose, but the sharpest line is defensive double-duty: removal-adjacent in effect without killing anything, just rearranging the combat step until the other player's attack stops adding up.