Myr Enforcer

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

Snow-Covered Mountain

Rustvale Bridge

Rustvale Bridge enters tapped.
Indestructible
{T}: Add {R} or {W}.

Galvanic Blast

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

Great Furnace

Experimental Synthesizer

When Experimental Synthesizer enters or leaves the battlefield, exile the top card of your library. Until end of turn, you may play that card.
{2}{R}, Sacrifice Experimental Synthesizer: Create a 2/2 white Samurai creature token with vigilance. Activate only as a sorcery.

Bone Saw

Equipped creature gets +1/+0.
Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)

Snow-Covered Plains

Ardent Recruit

Metalcraft — Ardent Recruit gets +2/+2 as long as you control three or more artifacts.

Ornithopter

Dueling Rapier

Flash
When Dueling Rapier enters, attach it to target creature you control.
Equipped creature gets +2/+0.
Equip {4} ({4}: Attach to target creature you control. Equip only as a sorcery.)

Blade-Tribe Berserkers

Metalcraft — When Blade-Tribe Berserkers enters, if you control three or more artifacts, Blade-Tribe Berserkers gets +3/+3 and gains haste until end of turn.

Auriok Sunchaser

Metalcraft — As long as you control three or more artifacts, Auriok Sunchaser gets +2/+2 and has flying.

Mirran Banesplitter

Flash
When Mirran Banesplitter enters, attach it to target creature you control.
Equipped creature gets +2/+0.
Equip {3} ({3}: Attach to target creature you control. Equip only as a sorcery.)

Golem-Skin Gauntlets

Equipped creature gets +1/+0 for each Equipment attached to it.
Equip {2} ({2}: Attach to target creature you control. Equip only as a sorcery. This card enters unattached and stays on the battlefield if the creature leaves.)

Ancient Den

Darksteel Citadel

Arcbound Mouser

Lifelink
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.)