Two-Headed Sliver

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

Gemhide Sliver

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

Sliver creatures you control have trample. (A creature with trample can deal excess combat damage to the player or planeswalker it's attacking.)

All Sliver creatures have frenzy 1. (Whenever a Sliver attacks and isn't blocked, it gets +1/+0 until end of turn.)

All Slivers have "{1}, Sacrifice this permanent: Each player discards a card."

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