Firewake Sliver

All Sliver creatures have haste.
All Slivers have "{1}, Sacrifice this permanent: Target Sliver creature gets +2/+2 until end of turn."

Striking Sliver

Sliver creatures you control have first strike. (They deal combat damage before creatures without first strike.)

Tempered Sliver

Sliver creatures you control have "Whenever this creature deals combat damage to a player, put a +1/+1 counter on it."

Mountain

Unclaimed Territory

As this land enters, choose a creature type.
{T}: Add {C}.
{T}: Add one mana of any color. Spend this mana only to cast a creature spell of the chosen type.

Gemhide Sliver

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

Megantic Sliver

Prizefight

Target creature you control fights target creature you don't control. (Each deals damage equal to its power to the other.)
Create a Treasure token. (It's an artifact with "{T}, Sacrifice this token: Add one mana of any color.")

Two-Headed Sliver

All Sliver creatures have menace. (They can't be blocked except by two or more creatures.)

Thrill of Possibility

As an additional cost to cast this spell, discard a card.
Draw two cards.

Predatory Sliver

Secluded Courtyard

As this land enters, choose a creature type.
{T}: Add {C}.
{T}: Add one mana of any color. Spend this mana only to cast a creature spell of the chosen type or activate an ability of a creature source of the chosen type.