Cheapest priced copy (The Dark): $9.49 at Card Kingdom, near mint, their price list as of .
Dark Sphere 
Artifact · Uncommon · The Dark · #100
{T}, Sacrifice this artifact: The next time a source of your choice would deal damage to you this turn, prevent half that damage, rounded down.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
1 printing · $9.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| The Dark | 100 | Uncommon | $9.49 | — |
One ruling from Wizards of the Coast
- 15 April 2013If two or more of these effects would apply, you apply them sequentially. So if the source would deal 5 damage after two of these abilities have resolved, the first one prevents 2 damage, reducing it to 3 damage, then the second one prevents a further 1 damage, reducing the total damage dealt to 2.