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."

Sliver creatures you control have vigilance. (Attacking doesn't cause them to tap.)

Enchant creature
Enchanted creature gets +2/+2, has reach, and is every creature type.

Etched Cornfield enters tapped unless a player has 13 or less life.
{T}: Add {G} or {W}.

Raucous Carnival enters tapped unless a player has 13 or less life.
{T}: Add {R} or {W}.

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

Thriving Heath enters tapped. As it enters, choose a color other than white.
{T}: Add {W} or one mana of the chosen color.

Create two 1/1 colorless Sliver creature tokens.

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

Thriving Bluff enters tapped. As it enters, choose a color other than red.
{T}: Add {R} or one mana of the chosen color.

Sliver creatures you control have double strike. (They deal both first-strike and regular combat damage.)

Sliver creatures you control have flying and haste.

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

Thriving Grove enters tapped. As it enters, choose a color other than green.
{T}: Add {G} or one mana of the chosen color.