Cheapest priced copy (Mirage): $0.99 at Card Kingdom, near mint, their price list as of .
Barreling Attack 
Instant · Rare · Mirage · #157
Target creature gains trample until end of turn. When that creature becomes blocked this turn, it gets +1/+1 until end of turn for each creature blocking it.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
1 printing · $0.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Mirage | 157 | Rare | $0.99 | — |
2 rulings from Wizards of the Coast
- 4 October 2004Both the +1/+1 and trample last only until end of turn.
- 1 May 2012Upon resolution, this gives the targeted creature trample and creates a delayed-triggered ability that will trigger when the creature becomes blocked. The creature will get +1/+1 for each creature blocking it as that ability resolves. This means that if Barreling Attack is cast after blockers are declared, the targeted creature will gain trample but won’t be able to get +1/+1 because it’s too late for the ability to trigger (unless there is another combat phase in the turn).