All Sliver creatures get +0/+2.
"I have spied them, wandering and watching—but for what? I fear they watch for us."
—Yonat of Amrou
(01/07/2013)
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.
(01/07/2013)
If the creature type of a Sliver changes 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.
(19/03/2021)
Because damage remains marked on a creature until the damage is removed as the turn ends, nonlethal damage dealt to another Sliver may become lethal if Watcher Sliver leaves the battlefield during that turn.
