MANAHIVE

“Act of Heroism” is the card you searched. White instants that untap a creature and pump stats are rare; most don’t grant all three effects. Closest equivalents:

• “Dauntless Onslaught” (W, Instant, untap not included, but gives +2/+2 to two targets until end of turn)
• “Emerge Unscathed” (W, Instant, gives protection, but no untap or +2/+2)
• “Valorous Stance” (W, Instant, gives indestructible or destroys a creature, but no untap/+2/+2)
• “Acrobatic Maneuver” (W, Instant, blinks creature/returns untapped, but no +2/+2 or block addition)

Reason: There isn’t a true white instant equivalent with all three effects together (untap, pump, and block multiple), but these are the closest in type and ability. Cards that specifically grant “can block an additional creature” are almost exclusive to “Act of Heroism” in white instants.