Heartfire Hero

Valiant — Whenever Heartfire Hero becomes the target of a spell or ability you control for the first time each turn, put a +1/+1 counter on it.
When Heartfire Hero dies, it deals damage equal to its power to each opponent.

Mabel, Heir to Cragflame

Other Mice you control get +1/+1.
When Mabel, Heir to Cragflame enters, create Cragflame, a legendary colorless Equipment artifact token with "Equipped creature gets +1/+1 and has vigilance, trample, and haste" and equip {2}.

Sacred Foundry

({T}: Add {R} or {W}.)
As Sacred Foundry enters, you may pay 2 life. If you don't, it enters tapped.

Sudden Breakthrough

Target creature gets +2/+0 and gains first strike until end of turn.
Create a Treasure token. (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.")

Rugged Prairie

{T}: Add {C}.
{R/W}, {T}: Add {R}{R}, {R}{W}, or {W}{W}.

Boros Garrison

Boros Garrison enters tapped.
When Boros Garrison enters, return a land you control to its owner's hand.
{T}: Add {R}{W}.

Battlefield Forge

{T}: Add {C}.
{T}: Add {R} or {W}. Battlefield Forge deals 1 damage to you.

Arid Mesa

{T}, Pay 1 life, Sacrifice Arid Mesa: Search your library for a Mountain or Plains card, put it onto the battlefield, then shuffle.

Fabled Passage

{T}, Sacrifice Fabled Passage: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle. Then if you control four or more lands, untap that land.

Inspiring Vantage

Inspiring Vantage enters tapped unless you control two or fewer other lands.
{T}: Add {R} or {W}.

Seedglaive Mentor

Vigilance, haste
Valiant — Whenever Seedglaive Mentor becomes the target of a spell or ability you control for the first time each turn, put a +1/+1 counter on it.

Thought Vessel

You have no maximum hand size.
{T}: Add {C}.

Whiskervale Forerunner

Valiant — Whenever Whiskervale Forerunner becomes the target of a spell or ability you control for the first time each turn, look at the top five cards of your library. You may reveal a creature card with mana value 3 or less from among them. You may put it onto the battlefield if it's your turn. If you don't put it onto the battlefield, put it into your hand. Put the rest on the bottom of your library in a random order.

Nettle Guard

Valiant — Whenever Nettle Guard becomes the target of a spell or ability you control for the first time each turn, it gets +0/+2 until end of turn.
{1}, Sacrifice Nettle Guard: Destroy target artifact or enchantment.

Command Tower

{T}: Add one mana of any color in your commander's color identity.

Sunscorched Divide

Brambleguard Captain

At the beginning of combat on your turn, target creature you control gets +X/+0 until end of turn, where X is Brambleguard Captain's power.

Mountain

Manifold Mouse

Offspring {2} (You may pay an additional {2} as you cast this spell. If you do, when this creature enters, create a 1/1 token copy of it.)
At the beginning of combat on your turn, target Mouse you control gains your choice of double strike or trample until end of turn.

Emberheart Challenger

Haste
Prowess (Whenever you cast a noncreature spell, this creature gets +1/+1 until end of turn.)
Valiant — Whenever Emberheart Challenger becomes the target of a spell or ability you control for the first time each turn, exile the top card of your library. Until end of turn, you may play that card.

Boros Signet

Pillarverge Pathway

Needleverge Pathway

Needleverge Pathway // Pillarverge Pathway

Talisman of Conviction

{T}: Add {C}.
{T}: Add {R} or {W}. Talisman of Conviction deals 1 damage to you.

Plains

Arcane Signet

Elegant Parlor

({T}: Add {R} or {W}.)
Elegant Parlor enters tapped.
When Elegant Parlor enters, surveil 1. (Look at the top card of your library. You may put it into your graveyard.)

Sundown Pass

Sundown Pass enters tapped unless you control two or more other lands.
{T}: Add {R} or {W}.

Sunbaked Canyon

{T}, Pay 1 life: Add {R} or {W}.
{1}, {T}, Sacrifice Sunbaked Canyon: Draw a card.

Whiskerquill Scribe

Valiant — Whenever Whiskerquill Scribe becomes the target of a spell or ability you control for the first time each turn, you may discard a card. If you do, draw a card.

Spectator Seating

Spectator Seating enters tapped unless you have two or more opponents.
{T}: Add {R} or {W}.

Mouse Trapper

Flash
Valiant — Whenever Mouse Trapper becomes the target of a spell or ability you control for the first time each turn, tap target creature an opponent controls.

Clifftop Retreat

Clifftop Retreat enters tapped unless you control a Mountain or a Plains.
{T}: Add {R} or {W}.

Ancestors' Aid

Eagles of the North

Flying
When Eagles of the North enters, creatures you control get +1/+0 and gain first strike until end of turn.
Plainscycling {1} ({1}, Discard this card: Search your library for a Plains card, reveal it, put it into your hand, then shuffle.)

Oliphaunt

Trample
Whenever Oliphaunt attacks, another target creature you control gets +2/+0 and gains trample until end of turn.
Mountaincycling {1} ({1}, Discard this card: Search your library for a Mountain card, reveal it, put it into your hand, then shuffle.)

Sol Ring

Reliquary Tower

Flowerfoot Swordmaster

Offspring {2} (You may pay an additional {2} as you cast this spell. If you do, when this creature enters, create a 1/1 token copy of it.)
Valiant — Whenever this creature becomes the target of a spell or ability you control for the first time each turn, Mice you control get +1/+0 until end of turn.

Ash Barrens

{T}: Add {C}.
Basic landcycling {1} ({1}, Discard this card: Search your library for a basic land card, reveal it, put it into your hand, then shuffle.)