Mana Echoes

Whenever a creature enters, you may add an amount of {C} equal to the number of creatures you control that share a creature type with it.

Izzet Signet

Plains

Gruul Signet

Sliver Queen

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

Island

Sliver Legion

All Sliver creatures get +1/+1 for each other Sliver on the battlefield.

Swamp

Arcane Signet

{T}: Add one mana of any color in your commander's color identity.

Squee, the Immortal

You may cast Squee, the Immortal from your graveyard or from exile.

Dimir Signet

Rakdos Signet

Orzhov Signet

Eternal Scourge

You may cast Eternal Scourge from exile.
When Eternal Scourge becomes the target of a spell or ability an opponent controls, exile Eternal Scourge.

Golgari Signet

Mountain

Sol Ring

Boros Signet

Food Chain

Exile a creature you control: Add X mana of any one color, where X is 1 plus the exiled creature's mana value. Spend this mana only to cast creature spells.

Simic Signet

Sliver Hivelord

Sliver creatures you control have indestructible. (Damage and effects that say "destroy" don't destroy them.)

Sliver Overlord

{3}: Search your library for a Sliver card, reveal that card, put it into your hand, then shuffle.
{3}: Gain control of target Sliver. (This effect lasts indefinitely.)

Azorius Signet

Forest

Cavern of Souls

As Cavern of Souls 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, and that spell can't be countered.

Selesnya Signet

Misthollow Griffin

Flying
You may cast Misthollow Griffin from exile.

The First Sliver

Cascade (When you cast this spell, exile cards from the top of your library until you exile a nonland card that costs less. You may cast it without paying its mana cost. Put the exiled cards on the bottom in a random order.)
Sliver spells you cast have cascade.

Sliver Hive

{T}: Add {C}.
{T}: Add one mana of any color. Spend this mana only to cast a Sliver spell.
{5}, {T}: Create a 1/1 colorless Sliver creature token. Activate only if you control a Sliver.