Ghalma's Warden

Metalcraft — Ghalma's Warden gets +2/+2 as long as you control three or more artifacts.

Myrsmith

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

Myr Battlesphere

When Myr Battlesphere enters, create four 1/1 colorless Myr artifact creature tokens.
Whenever Myr Battlesphere attacks, you may tap X untapped Myr you control. If you do, Myr Battlesphere gets +X/+0 until end of turn and deals X damage to the player or planeswalker it's attacking.

Darksteel Myr

Indestructible (Damage and effects that say "destroy" don't destroy this creature. If its toughness is 0 or less, it's still put into its owner's graveyard.)

Palladium Myr

Seize the Initiative

Target creature gets +1/+1 and gains first strike until end of turn.

Auriok Edgewright

Metalcraft — Auriok Edgewright has double strike as long as you control three or more artifacts.

Inspired Charge

Creatures you control get +2/+1 until end of turn.

Revoke Existence

Plains

Perilous Myr

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

Darksteel Sentinel

Flash (You may cast this spell any time you could cast an instant.)
Vigilance
Indestructible (Damage and effects that say "destroy" don't destroy this creature. If its toughness is 0 or less, it's still put into its owner's graveyard.)

Sunblast Angel

Flying
When Sunblast Angel enters, destroy all tapped creatures.

Razor Hippogriff

Flying
When Razor Hippogriff enters, return target artifact card from your graveyard to your hand. You gain life equal to that card's mana value.

Myr Galvanizer

Other Myr creatures you control get +1/+1.
{1}, {T}: Untap each other Myr you control.

Gold Myr

Origin Spellbomb

{1}, {T}, Sacrifice Origin Spellbomb: Create a 1/1 colorless Myr artifact creature token.
When Origin Spellbomb is put into a graveyard from the battlefield, you may pay {W}. If you do, draw a card.

Dispense Justice

Target player sacrifices an attacking creature of their choice.
Metalcraft — That player sacrifices two attacking creatures of their choice instead if you control three or more artifacts.

Arrest

Enchant creature
Enchanted creature can't attack or block, and its activated abilities can't be activated.