Arcane Signet

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

Sidisi, Brood Tyrant

Whenever Sidisi, Brood Tyrant enters or attacks, mill three cards.
Whenever one or more creature cards are put into your graveyard from your library, create a 2/2 black Zombie creature token.

Sakashima of a Thousand Faces

You may have Sakashima of a Thousand Faces enter as a copy of another creature you control, except it has Sakashima of a Thousand Faces's other abilities.
The "legend rule" doesn't apply to permanents you control.
Partner (You can have two commanders if both have partner.)

The Mimeoplasm

As The Mimeoplasm enters, you may exile two creature cards from graveyards. If you do, it enters as a copy of one of those cards with a number of additional +1/+1 counters on it equal to the power of the other card.

Bloom Tender

{T}: For each color among permanents you control, add one mana of that color.

Sphinx of Lost Truths

Kicker {1}{U} (You may pay an additional {1}{U} as you cast this spell.)
Flying
When Sphinx of Lost Truths enters, draw three cards. Then if it wasn't kicked, discard three cards.

Birds of Paradise

Chromatic Lantern

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

Biowaste Blob

Oozes you control get +1/+1.
At the beginning of your upkeep, if you control a commander, create a token that's a copy of Biowaste Blob.

Wonder

Flying
As long as Wonder is in your graveyard and you control an Island, creatures you control have flying.

Lord of Extinction

Lord of Extinction's power and toughness are each equal to the number of cards in all graveyards.

Sakashima the Impostor

You may have Sakashima the Impostor enter as a copy of any creature on the battlefield, except its name is Sakashima the Impostor, it's legendary in addition to its other types, and it has "{2}{U}{U}: Return this creature to its owner's hand at the beginning of the next end step."

Buried Alive

Search your library for up to three creature cards, put them into your graveyard, then shuffle.

Sol Ring

Entomb

Search your library for a card, put that card into your graveyard, then shuffle.