Plains

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.

Myrsmith

Whenever you cast an artifact spell, you may pay {1}. If you do, create a 1/1 colorless Myr artifact creature token.

Tempered Steel

Artifact creatures you control get +2/+2.

Steel Overseer

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

Golem's Heart

Whenever a player casts an artifact spell, you may gain 1 life.

Memnite

Mox Opal

Metalcraft — {T}: Add one mana of any color. Activate only if you control three or more artifacts.

Ancient Den

Glint Hawk

Flying
When Glint Hawk enters the battlefield, sacrifice it unless you return an artifact you control to its owner's hand.

Dispatch

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

Perilous Myr

When Perilous Myr dies, it deals 2 damage to any target.

Etched Champion

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