Hargilde, Kindly Runechanter

{T}: Add {C}{C}. Spend this mana only to cast artifact spells or activate abilities of artifacts.
Friends forever (You can have two commanders if both have friends forever.)

Luxury Suite

Luxury Suite enters tapped unless you have two or more opponents.
{T}: Add {B} or {R}.

Urborg, Tomb of Yawgmoth

Each land is a Swamp in addition to its other land types.

Cecily, Haunted Mage

Your maximum hand size is eleven.
Whenever Cecily, Haunted Mage attacks, you draw a card and you lose 1 life. Then if you have eleven or more cards in your hand, you may cast an instant or sorcery spell from your hand without paying its mana cost.
Friends forever (You can have two commanders if both have friends forever.)

Morphic Pool

Morphic Pool enters tapped unless you have two or more opponents.
{T}: Add {U} or {B}.

Vault of Champions

Vault of Champions enters tapped unless you have two or more opponents.
{T}: Add {W} or {B}.

Arcane Signet

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

Lotus Petal

{T}, Sacrifice Lotus Petal: Add one mana of any color.

Spectator Seating

Spectator Seating enters tapped unless you have two or more opponents.
{T}: Add {R} or {W}.

Sea of Clouds

Sea of Clouds enters tapped unless you have two or more opponents.
{T}: Add {W} or {U}.

Training Center

Training Center enters tapped unless you have two or more opponents.
{T}: Add {U} or {R}.

Goblin Welder

{T}: Choose target artifact a player controls and target artifact card in that player's graveyard. If both targets are still legal as this ability resolves, that player simultaneously sacrifices the artifact and returns the artifact card to the battlefield.

Sol Ring

Mesmeric Orb

Whenever a permanent becomes untapped, that permanent's controller mills a card.

Basalt Monolith

Basalt Monolith doesn't untap during your untap step.
{T}: Add {C}{C}{C}.
{3}: Untap Basalt Monolith.