Cheapest priced copy (Mirage): $1.49 at Card Kingdom, near mint, their price list as of .
Null Chamber 
World Enchantment · Rare · Mirage · #31
As this enchantment enters, you and an opponent each choose a card name other than a basic land card name.
Spells with the chosen names can't be cast and lands with the chosen names can't be played.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
1 printing · $1.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Mirage | 31 | Rare | $1.49 | — |
3 rulings from Wizards of the Coast
- 1 February 2006If you somehow manage to cast this while other spells are on the stack, those spells won't be countered.
- 1 October 2008This has the supertype world. When a world permanent enters, any world permanents that were already on the battlefield are put into their owners' graveyards. This is a state-based action called the "world rule." The new world permanent stays on the battlefield. If two world permanents enter at the same time, they're both put into their owners' graveyards.
- 15 April 2013You choose which opponent makes the choice. Null Chamber does not target that opponent.