July 1, 2013 Wizards of the Coast
If you control multiple Thorncaster Slivers and a Sliver you control attacks, each ability will trigger separately.
July 1, 2013 Wizards of the Coast
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.
July 1, 2013 Wizards of the Coast
Abilities that Slivers grant, as well as power/toughness boosts, are cumulative. However, for some abilities, like flying, having more than one instance of the ability doesn’t provide any additional benefit.

Other Printings

Secret Lair Drop (sld)