Into Thin Air

Affinity for artifacts (This spell costs {1} less to cast for each artifact you control.)
Return target artifact to its owner's hand.

Assert Authority

Affinity for artifacts (This spell costs {1} less to cast for each artifact you control.)
Counter target spell. If that spell is countered this way, exile it instead of putting it into its owner's graveyard.

Thoughtcast

Affinity for artifacts (This spell costs {1} less to cast for each artifact you control.)
Draw two cards.

Ancient Den

Mycosynth Golem

Affinity for artifacts (This spell costs {1} less to cast for each artifact you control.)
Artifact creature spells you cast have affinity for artifacts. (They cost {1} less to cast for each artifact you control.)

Ancient Tomb

{T}: Add {C}{C}. Ancient Tomb deals 2 damage to you.

Vault of Whispers

Welding Jar

Sacrifice Welding Jar: Regenerate target artifact.

Darksteel Citadel

Broodstar

Affinity for artifacts (This spell costs {1} less to cast for each artifact you control.)
Flying
Broodstar's power and toughness are each equal to the number of artifacts you control.

Memnite

Memnarch

{1}{U}{U}: Target permanent becomes an artifact in addition to its other types. (This effect lasts indefinitely.)
{3}{U}: Gain control of target artifact. (This effect lasts indefinitely.)

Seat of the Synod

Mycosynth Lattice

All permanents are artifacts in addition to their other types.
All cards that aren't on the battlefield, spells, and permanents are colorless.
Players may spend mana as though it were mana of any color.

Karn, the Great Creator

Activated abilities of artifacts your opponents control can't be activated.
+1: Until your next turn, up to one target noncreature artifact becomes an artifact creature with power and toughness each equal to its mana value.
−2: You may reveal an artifact card you own from outside the game or choose a face-up artifact card you own in exile. Put that card into your hand.

Myr Retriever

When Myr Retriever dies, return another target artifact card from your graveyard to your hand.

Darksteel Juggernaut

Indestructible
Darksteel Juggernaut's power and toughness are each equal to the number of artifacts you control.
Darksteel Juggernaut attacks each combat if able.

Chromescale Drake

Affinity for artifacts (This spell costs {1} less to cast for each artifact you control.)
Flying
When Chromescale Drake enters the battlefield, reveal the top three cards of your library. Put all artifact cards revealed this way into your hand and the rest into your graveyard.