Cheapest priced copy (Commander 2013): $0.35 at Card Kingdom, near mint, their price list as of .
Curse of Predation 
Enchantment — Aura Curse · Uncommon · Commander 2013 · #140
Enchant player
Whenever a creature attacks enchanted player, put a +1/+1 counter on it.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
4 printings · $0.35 to $1.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander 2013 | 140 | Uncommon | $0.35 | — |
| Commander Anthology | 99 | Uncommon | $0.35 | — |
| Iconic Masters | 159 | Rare | $0.49 | $1.99 |
| The List | C13-140 | Uncommon | $0.35 | — |
5 rulings from Wizards of the Coast
- 17 October 2013Curse is an enchantment type, not a creature type (or any other kind of subtype).
- 17 October 2013The ability won’t trigger when a creature attacks a planeswalker controlled by the enchanted player.
- 17 October 2013Each of the Curses can be attached to any player, including the player who cast the Curse.
- 17 October 2013A Curse spell targets the player it will enchant like any other Aura spell, and a Curse stays on the battlefield like any other Aura. If the enchanted player gains protection from the Curse’s color (or any other characteristic the Curse has), the Curse will be put into its owner’s graveyard.
- 17 October 2013The Curse subtype has no inherent rules meaning, but two cards in the Innistrad set (Bitterheart Witch and Witchbane Orb) refer to Curses.