Root Sliver | Magic: The Gathering
Formats Root Sliver is Legal in
Official Oracle Text for Root Sliver
Sliver spells can't be countered by spells or abilities.
—Riptide Project researcher
Official Rulings for Root Sliver
4/1/2008 : The addition of "by spells or abilities" to the second ability is so that tribal instant or sorcery spells that happen to be Slivers (such as Crib Swap) can be countered by the rules if all of their targets become illegal.
7/1/2013 : 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.
7/1/2013 : 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.