Diffusion Sliver

• WWizards of the Coast2014-07-18
  Official Ruling
  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.
• WWizards of the Coast2014-07-18
  Official Ruling
  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.
• WWizards of the Coast2014-07-18
  Official Ruling
  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.
• WWizards of the Coast2014-07-18
  Official Ruling
  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.

Rulings via Scryfall