Cheapest priced copy (War of the Spark): $0.35 at Card Kingdom, near mint, their price list as of .
Gideon's Triumph 
Instant · Uncommon · War of the Spark · #15
Target opponent sacrifices a creature of their choice that attacked or blocked this turn. If you control a Gideon planeswalker, that player sacrifices two of those creatures of their choice instead.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| War of the Spark | 15 | Uncommon | $0.35 | $0.49 |
7 rulings from Wizards of the Coast
- 3 May 2019Gideon’s Triumph targets the player, not the creature or creatures to be sacrificed. A creature with hexproof may be sacrificed this way.
- 3 May 2019A creature that was put onto the battlefield attacking didn’t attack, so it can’t be sacrificed.
- 3 May 2019Controlling more than one planeswalker of the appropriate type won’t have any more of a benefit than just controlling one.
- 3 May 2019Whether you control an appropriate planeswalker is checked only as the spell resolves.
- 3 May 2019A creature that attacked and was removed from combat (such as by Spires of Orazca) still attacked, so it can be sacrificed.
- 3 May 2019Gideon’s Triumph can be cast after combat damage has been dealt. In this case, the target player chooses one or two creatures that attacked or blocked this turn and have survived combat damage.
- 3 May 2019Gideon’s Triumph can be cast before combat damage has been dealt. In this case, it can be cast before or after blockers have been chosen.