Martyr's Soul

Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.)
When Martyr's Soul enters, if you control no tapped lands, put two +1/+1 counters on it.

Rally the Peasants

Creatures you control get +2/+0 until end of turn.
Flashback {2}{R} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Ancient Den

Galvanic Blast

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

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.

Rustvale Bridge

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

Candy Trail

When Candy Trail enters, scry 2.
{2}, {T}, Sacrifice Candy Trail: You gain 3 life and draw a card.

Ardent Recruit

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

Mountain

Glint Hawk

Flying
When Glint Hawk enters, sacrifice it unless you return an artifact you control to its owner's hand.

Forgotten Cave

Forgotten Cave enters tapped.
{T}: Add {R}.
Cycling {R} ({R}, Discard this card: Draw a card.)

Plains

Great Furnace

Clowning Around

Create two 1/1 white Clown Robot artifact creature tokens, then roll a six-sided die. If the result is equal to or less than the number of Robots you control, create a 1/1 white Clown Robot artifact creature token.

Lightning Bolt

Lightning Bolt deals 3 damage to any target.

Myr Enforcer

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

Secluded Steppe

Secluded Steppe enters tapped.
{T}: Add {W}.
Cycling {W} ({W}, Discard this card: Draw a card.)

Kor Skyfisher

Flying
When Kor Skyfisher enters, return a permanent you control to its owner's hand.