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.

Mountain

Master of Etherium

Master of Etherium's power and toughness are each equal to the number of artifacts you control.
Other artifact creatures you control get +1/+1.

Seachrome Coast

Seachrome Coast enters tapped unless you control two or fewer other lands.
{T}: Add {W} or {U}.

Springleaf Drum

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

Memnite

Island

Dispatch

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

Toolcraft Exemplar

At the beginning of combat on your turn, if you control an artifact, Toolcraft Exemplar gets +2/+1 until end of turn. If you control three or more artifacts, it also gains first strike until end of turn.

Grafdigger's Cage

Creature cards in graveyards and libraries can't enter the battlefield.
Players can't cast spells from graveyards or libraries.

Galvanic Blast

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

Cranial Plating

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

Built to Last

Target creature gets +2/+2 until end of turn. If it's an artifact creature, it gains indestructible until end of turn. (Damage and effects that say "destroy" don't destroy it.)

Frogmite

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

Ornithopter

Inspiring Vantage

Inspiring Vantage enters tapped unless you control two or fewer other lands.
{T}: Add {R} or {W}.

Darksteel Citadel

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.)

Ensoul Artifact

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

Ghirapur Aether Grid

Tap two untapped artifacts you control: Ghirapur Aether Grid deals 1 damage to any target.