Etched Champion

Metalcraft — Etched Champion has protection from each color as long as you control three or more artifacts.

Tempered Steel

Artifact creatures you control get +2/+2.

Silver Myr

Gold Myr

Puresteel Paladin

Whenever an Equipment you control enters, you may draw a card.
Metalcraft — Equipment you control have equip {0} as long as you control three or more artifacts.

Island

Dissipation Field

Whenever a permanent deals damage to you, return it to its owner's hand.

Venser's Journal

You have no maximum hand size.
At the beginning of your upkeep, you gain 1 life for each card in your hand.

Razortide Bridge

Razortide Bridge enters tapped.
Indestructible
{T}: Add {W} or {U}.

Plains

Darksteel Citadel

Kami of False Hope

Sacrifice Kami of False Hope: Prevent all combat damage that would be dealt this turn.

Steel Overseer

{T}: Put a +1/+1 counter on each artifact creature you control.

Darksteel Forge

Artifacts you control have indestructible. (Effects that say "destroy" don't destroy them. Artifact creatures with indestructible can't be destroyed by damage.)

Palladium Myr

Stoic Rebuttal

Metalcraft — This spell costs {1} less to cast if you control three or more artifacts.
Counter target spell.

Darksteel Axe

Indestructible (Effects that say "destroy" don't destroy this artifact.)
Equipped creature gets +2/+0.
Equip {2}

Dispense Justice

Target player sacrifices an attacking creature.
Metalcraft — That player sacrifices two attacking creatures instead if you control three or more artifacts.

Indomitable Archangel

Flying
Metalcraft — Artifacts you control have shroud as long as you control three or more artifacts. (An artifact with shroud can't be the target of spells or abilities.)

Cranial Plating

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

Argent Sphinx

Flying
Metalcraft — {U}: Exile Argent Sphinx. Return it to the battlefield under your control at the beginning of the next end step. Activate only if you control three or more artifacts.

Dispatch

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

Ornithopter

Memnite

Argentum Armor

Equipped creature gets +6/+6.
Whenever equipped creature attacks, destroy target permanent.
Equip {6}