Manaweft Sliver

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

Biomancer's Familiar

Activated abilities of creatures you control cost {2} less to activate. This effect can't reduce the mana in that cost to less than one mana.
{T}: The next time target creature adapts this turn, it adapts as though it had no +1/+1 counters on it.

Training Grounds

Activated abilities of creatures you control cost {2} less to activate. This effect can't reduce the mana in that cost to less than one mana.

Heartstone

Activated abilities of creatures cost {1} less to activate. This effect can't reduce the mana in that cost to less than one mana.

Agatha of the Vile Cauldron

Activated abilities of creatures you control cost {X} less to activate, where X is Agatha of the Vile Cauldron's power. This effect can't reduce the mana in that cost to less than one mana.
{4}{R}{G}: Other creatures you control get +1/+1 and gain trample and haste until end of turn.

Ashnod's Altar

Cloudshredder Sliver

Sliver creatures you control have flying and haste.

Basal Sliver

All Slivers have "Sacrifice this permanent: Add {B}{B}."

Sliver Queen

{2}: Create a 1/1 colorless Sliver creature token.

Zirda, the Dawnwaker

Companion — Each permanent card in your starting deck has an activated ability. (If this card is your chosen companion, you may put it into your hand from outside the game for {3} as a sorcery.)
Abilities you activate that aren't mana abilities cost {2} less to activate. This effect can't reduce the mana in that cost to less than one mana.
{1}, {T}: Target creature can't block this turn.

Homing Sliver

Each Sliver card in each player's hand has slivercycling {3}.
Slivercycling {3} ({3}, Discard this card: Search your library for a Sliver card, reveal it, put it into your hand, then shuffle.)