Cheapest priced copy (Magic 2015): $2.79 at Card Kingdom, near mint, their price list as of .
Diffusion Sliver 
Creature — Sliver · 1/1 · Uncommon · Magic 2015 · #50
Whenever a Sliver creature you control becomes the target of a spell or ability an opponent controls, counter that spell or ability unless its controller pays {2}.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
3 printings · $2.79 to $9.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander Masters | 845 | Uncommon | $4.99 | — |
| Magic 2015 | 50 | Uncommon | $2.79 | $9.99Out of stock |
| Secret Lair Drop | 618 | Rare | — | $9.49 |
4 rulings from Wizards of the Coast
- 18 July 2014The granted ability applies to any spell (including Aura spells), activated ability, or triggered ability that’s controlled by an opponent that targets a Sliver you control.
- 18 July 2014If you change the creature type of a Sliver you control so it’s no longer a Sliver, it will no longer be affected by its own ability. Its ability will continue to affect other Sliver creatures you control.
- 18 July 2014Slivers in this set affect only Sliver creatures you control. They don’t grant bonuses to your opponents’ Slivers. This is the same way Slivers from the Magic 2014 core set worked, while Slivers in earlier sets granted bonuses to all Slivers.
- 18 July 2014Abilities that Slivers grant, as well as power/toughness boosts, are cumulative. However, for some abilities, like indestructible and the ability granted by Belligerent Sliver, having more than one instance of the ability doesn’t provide any additional benefit.