Untap target creature. It gets +2/+2 until end of turn and can block an additional creature this turn.
3/16/2018 You can cast Act of Heroism even if the target creature won’t be able to block right away, perhaps because you’re the attacking player.
3/16/2018 Untapping an attacking creature doesn’t remove it from combat.
3/16/2018 Act of Heroism can target an untapped creature. It still gets +2/+2 and can block an additional creature.
3/16/2018 The effects of Act of Heroism are cumulative. If multiples resolve targeting the same creature, that creature can block that many additional creatures this turn.