Mountain

Darksteel Axe

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

Blade-Tribe Berserkers

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

Embersmith

Whenever you cast an artifact spell, you may pay {1}. If you do, this creature deals 1 damage to any target.

Trinket Mage

When this creature enters, you may search your library for an artifact card with mana value 1 or less, reveal that card, put it into your hand, then shuffle.

Golem Foundry

Whenever you cast an artifact spell, you may put a charge counter on this artifact.
Remove three charge counters from this artifact: Create a 3/3 colorless Golem artifact creature token.

Memnite

Riddlesmith

Whenever you cast an artifact spell, you may draw a card. If you do, discard a card.

Argent Sphinx

Flying
Metalcraft — {U}: Exile this creature. 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.

Galvanic Blast

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

Echo Circlet

Equipped creature can block an additional creature each combat.
Equip {1}

Island

Sylvok Lifestaff

Equipped creature gets +1/+0.
Whenever equipped creature dies, you gain 3 life.
Equip {1}

Silver Myr

Accorder's Shield

Equipped creature gets +0/+3 and has vigilance. (Attacking doesn't cause it to tap.)
Equip {3} ({3}: Attach to target creature you control. Equip only as a sorcery.)

Etched Champion

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

Golem's Heart

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

Iron Myr

Disperse

Return target nonland permanent to its owner's hand.

Rusted Relic

Metalcraft — This artifact is a 5/5 Golem artifact creature as long as you control three or more artifacts.

Lumengrid Drake

Flying
Metalcraft — When this creature enters, if you control three or more artifacts, return target creature to its owner's hand.

Chrome Steed

Metalcraft — This creature gets +2/+2 as long as you control three or more artifacts.

Snapsail Glider

Metalcraft — This creature has flying as long as you control three or more artifacts.