Cheapest priced copy (Dragons of Tarkir): $0.35 at Card Kingdom, near mint, their price list as of .
Ruthless Deathfang 
Creature — Dragon · 4/4 · Uncommon · Dragons of Tarkir · #229
Flying
Whenever you sacrifice a creature, target opponent sacrifices a creature of their choice.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
2 printings · $0.35 to $0.79 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Dragons of Tarkir | 229 | Uncommon | $0.35 | $0.79 |
| Midnight Hunt Commander | 154 | Uncommon | $0.35 | — |
2 rulings from Wizards of the Coast
- 25 February 2015Notably, the “legend rule” does not cause any permanents to be sacrificed. They are simply put into their owners' graveyards.
- 25 February 2015Ruthless Deathfang's triggered ability will trigger whenever you sacrifice any creature, including Ruthless Deathfang itself. It will trigger whenever you sacrifice a creature for any reason, including to pay a cost or as the result of a spell or ability (such as an opposing Ruthless Deathfang's ability).