Cheapest priced copy (Mystery Booster 2): $2.49 at Card Kingdom, near mint, their price list as of .
Pox 
Sorcery · Rare · Ice Age · #158
Each player loses a third of their life, then discards a third of the cards in their hand, then sacrifices a third of the creatures they control of their choice, then sacrifices a third of the lands they control of their choice. Round up each time.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
4 printings · $2.49 to $19.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Fifth Edition | 189 | Rare | $5.49 | — |
| Ice Age | 158 | Rare | $8.99 | — |
| Mystery Booster 2 | 185 | Rare | $2.49 | $19.99 |
| Oversized League Prizes | 63 | Rare | — | — |
3 rulings from Wizards of the Coast
- 16 September 2007The number you need to lose, discard, or sacrifice isn't calculated until it's time to perform that part of the effect. For example, if your opponent casts Pox and you discard Dodecapod as part of Pox's discard effect, Dodecapod will be put onto the battlefield instead of into your graveyard. Then, when determining how many creatures you need to sacrifice, the Dodecapod is taken into account.
- 16 September 2007The losses, discards, and sacrifices are rounded up. For example, if you have 5 life, you'll lose 2 life, leaving you at 3 life. (Five divided by three is one and two-thirds. Rounding that up to the nearest whole number gives you two.)
- 16 September 2007Each part of Pox's effect is processed separately. For each part, first the player whose turn it is makes all necessary choices (such as which cards to discard), then each other player in turn order chooses, then the actions happen at the same time. Then Pox's effect moves to the next stage.