Siege Mastodon

Razorfield Rhino

Metalcraft — Razorfield Rhino gets +2/+2 as long as you control three or more artifacts.

Whispersilk Cloak

Equipped creature can't be blocked and has shroud. (It can't be the target of spells or abilities.)
Equip {2}

Accorder Paladin

Battle cry (Whenever this creature attacks, each other attacking creature gets +1/+0 until end of turn.)

Iron Myr

Ardent Recruit

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

White Sun's Zenith

Create X 2/2 white Cat creature tokens. Shuffle White Sun's Zenith into its owner's library.

Gold Myr

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.

Arrest

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

Master's Call

Create two 1/1 colorless Myr artifact creature tokens.

Kuldotha Ringleader

Battle cry (Whenever this creature attacks, each other attacking creature gets +1/+0 until end of turn.)
Kuldotha Ringleader attacks each combat if able.

Viridian Claw

Equipped creature gets +1/+0 and has first strike.
Equip {1}

Silvercoat Lion

Concussive Bolt

Concussive Bolt deals 4 damage to target player or planeswalker.
Metalcraft — If you control three or more artifacts, creatures controlled by that player or by that planeswalker's controller can't block this turn.

Plains

Myrsmith

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

Memnite

Mountain

Leonin Relic-Warder

When Leonin Relic-Warder enters, you may exile target artifact or enchantment.
When Leonin Relic-Warder leaves the battlefield, return the exiled card to the battlefield under its owner's control.

Peace Strider

When Peace Strider enters, you gain 3 life.

Victory's Herald

Flying
Whenever Victory's Herald attacks, attacking creatures gain flying and lifelink until end of turn.

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.

Galvanic Blast

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