Diffusion Sliver

Oracle Text

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.

Card Rulings

7/18/2014 The 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.
7/18/2014 Slivers 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.
7/18/2014 Abilities 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.
7/18/2014 If 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.

Additional Information