Counterspell

Venom Sliver

Sliver creatures you control have deathtouch. (Any amount of damage a creature with deathtouch deals to a creature is enough to destroy it.)

Farseek

Search your library for a Plains, Island, Swamp, or Mountain card, put it onto the battlefield tapped, then shuffle.

Harmonic Sliver

All Slivers have "When this permanent enters, destroy target artifact or enchantment."

Gemhide Sliver

All Slivers have "{T}: Add one mana of any color."

Cloudshredder Sliver

Sliver creatures you control have flying and haste.

Three Visits

Search your library for a Forest card, put it onto the battlefield, then shuffle.

Three Tree City

As Three Tree City enters, choose a creature type.
{T}: Add {C}.
{2}, {T}: Choose a color. Add an amount of mana of that color equal to the number of creatures you control of the chosen type.

Path to Exile

Exile target creature. Its controller may search their library for a basic land card, put that card onto the battlefield tapped, then shuffle.

Patchwork Banner

As Patchwork Banner enters, choose a creature type.
Creatures you control of the chosen type get +1/+1.
{T}: Add one mana of any color.

Blur Sliver

Sliver creatures you control have haste. (They can attack and {T} as soon as they come under your control.)

Negate

Shifting Sliver

Slivers can't be blocked except by Slivers.

Rampant Growth

Search your library for a basic land card, put that card onto the battlefield tapped, then shuffle.

Horned Sliver

Syphon Sliver

Sliver creatures you control have lifelink. (Damage dealt by a Sliver creature you control also causes you to gain that much life.)

Sliver Hivelord

Sliver creatures you control have indestructible. (Damage and effects that say "destroy" don't destroy them.)

Manaweft Sliver

Sliver creatures you control have "{T}: Add one mana of any color."

Swords to Plowshares

Exile target creature. Its controller gains life equal to its power.

Nature's Lore

Search your library for a Forest card, put that card onto the battlefield, then shuffle.

Sinew Sliver

Sliver Legion

All Sliver creatures get +1/+1 for each other Sliver on the battlefield.

Crystalline Sliver

All Slivers have shroud. (They can't be the targets of spells or abilities.)

Cultivate

Search your library for up to two basic land cards, reveal those cards, put one onto the battlefield tapped and the other into your hand, then shuffle.