Cheapest priced copy (Khans of Tarkir): $0.79 at Card Kingdom, near mint, their price list as of .
Mardu Ascendancy 
Enchantment · Rare · Khans of Tarkir · #185
Whenever a nontoken creature you control attacks, create a 1/1 red Goblin creature token that's tapped and attacking.
Sacrifice this enchantment: Creatures you control get +0/+3 until end of turn.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
2 printings · $0.79 to $5.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Khans of Tarkir | 185 | Rare | $0.79 | $1.99 |
| Khans of Tarkir Promos | 185s | Rare | — | $5.99 |
2 rulings from Wizards of the Coast
- 20 September 2014Although the tokens are attacking, they were never declared as attacking creatures (for purposes of abilities that trigger whenever a creature attacks, for example).
- 20 September 2014As the Goblin token enters the battlefield, you choose which opponent or opposing planeswalker it’s attacking. It doesn’t have to attack the same opponent or opposing planeswalker that the original creature is attacking.