Virulent Sliver

All Sliver creatures have poisonous 1. (Whenever a Sliver deals combat damage to a player, that player gets a poison counter. A player with ten or more poison counters loses the game.)

Forest

Mindlash Sliver

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

Harmonize

Liege of the Pit

Flying, trample
At the beginning of your upkeep, sacrifice a creature other than Liege of the Pit. If you can't, Liege of the Pit deals 7 damage to you.
Morph {B}{B}{B}{B} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)

Spinneret Sliver

Akroma, Angel of Wrath

Flying, first strike, vigilance, trample, haste, protection from black and from red

Akroma, Angel of Fury

This spell can't be countered.
Flying, trample, protection from white and from blue
{R}: Akroma, Angel of Fury gets +1/+0 until end of turn.
Morph {3}{R}{R}{R} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)

Strangling Soot

Destroy target creature with toughness 3 or less.
Flashback {5}{R} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Gemhide Sliver

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

Slaughter Pact

Destroy target nonblack creature.
At the beginning of your next upkeep, pay {2}{B}. If you don't, you lose the game.