As malleable as molten steel, but as dangerous as the finished blade.

Magma Sliver

All Slivers have "{T}: Target Sliver creature gets +X/+0 until end of turn, where X is the number of Slivers on the battlefield."

Secret Lair Drop

Salvat 2005

Legions

All Slivers have "{T}: Target Sliver gets +X/+0 until end of turn, where X is the number of Slivers in play."

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.

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.