Steel Overseer

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

Hallowed Fountain

({T}: Add {W} or {U}.)
As Hallowed Fountain enters, you may pay 2 life. If you don't, it enters tapped.

Ornithopter

Thoughtcast

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

Plains

Tempered Steel

Artifact creatures you control get +2/+2.

Etched Champion

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

Court Homunculus

Court Homunculus gets +1/+1 as long as you control another artifact.

Arcbound Crusher

Trample
Whenever another artifact enters, put a +1/+1 counter on Arcbound Crusher.
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.)

Mishra's Factory

{T}: Add {C}.
{1}: Mishra's Factory becomes a 2/2 Assembly-Worker artifact creature until end of turn. It's still a land.
{T}: Target Assembly-Worker creature gets +1/+1 until end of turn.

Gingerbrute

Haste
{1}: Gingerbrute can't be blocked this turn except by creatures with haste.
{2}, {T}, Sacrifice Gingerbrute: You gain 3 life.

Memnite

Myr Enforcer

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

Island

Inquisitive Puppet

When Inquisitive Puppet enters, scry 1.
Exile Inquisitive Puppet: Create a 1/1 white Human creature token.