Darksteel Citadel

Dispatch

Tap target creature.
Metalcraft — If you control three or more artifacts, exile that creature.

Signal Pest

Battle cry (Whenever this creature attacks, each other attacking creature gets +1/+0 until end of turn.)
Signal Pest can't be blocked except by creatures with flying or reach.

Thoughtcast

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

Bomat Courier

Haste
Whenever Bomat Courier attacks, exile the top card of your library face down. (You can't look at it.)
{R}, Discard your hand, Sacrifice Bomat Courier: Put all cards exiled with Bomat Courier into their owners' hands.

Stubborn Denial

Counter target noncreature spell unless its controller pays {1}.
Ferocious — If you control a creature with power 4 or greater, counter that spell instead.

Metallic Rebuke

Improvise (Your artifacts can help cast this spell. Each artifact you tap after you're done activating mana abilities pays for {1}.)
Counter target spell unless its controller pays {3}.

Whipflare

Whipflare deals 2 damage to each nonartifact creature.

Glimmervoid

At the beginning of the end step, if you control no artifacts, sacrifice Glimmervoid.
{T}: Add one mana of any color.

Chronomaton

{1}, {T}: Put a +1/+1 counter on Chronomaton.

Cranial Plating

Equipped creature gets +1/+0 for each artifact you control.
{B}{B}: Attach Cranial Plating to target creature you control.
Equip {1}

Springleaf Drum

{T}, Tap an untapped creature you control: Add one mana of any color.

Shrapnel Blast

As an additional cost to cast this spell, sacrifice an artifact.
Shrapnel Blast deals 5 damage to any target.

Ornithopter

Arcbound Worker

Modular 1 (This creature enters with a +1/+1 counter on it. When it dies, you may put its +1/+1 counters on target artifact creature.)

Fragmentize

Destroy target artifact or enchantment with mana value 4 or less.

Ensoul Artifact

Enchant artifact
Enchanted artifact is a creature with base power and toughness 5/5 in addition to its other types.

Tormod's Crypt

{T}, Sacrifice Tormod's Crypt: Exile target player's graveyard.

Vault Skirge

({B/P} can be paid with either {B} or 2 life.)
Flying
Lifelink (Damage dealt by this creature also causes you to gain that much life.)

Welding Jar

Sacrifice Welding Jar: Regenerate target artifact.

Island

Memnite

Galvanic Blast

Galvanic Blast deals 2 damage to any target.
Metalcraft — Galvanic Blast deals 4 damage instead if you control three or more artifacts.

Spire of Industry

{T}: Add {C}.
{T}, Pay 1 life: Add one mana of any color. Activate only if you control an artifact.

Spreading Seas

Enchant land
When Spreading Seas enters, draw a card.
Enchanted land is an Island.