Dreadhorde Arcanist

Trample
Whenever Dreadhorde Arcanist attacks, you may cast target instant or sorcery card with mana value less than or equal to Dreadhorde Arcanist's power from your graveyard without paying its mana cost. If that spell would be put into your graveyard, exile it instead.

Steam Vents

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

Defiant Strike

Target creature gets +1/+0 until end of turn.
Draw a card.

Sulfur Falls

Sulfur Falls enters tapped unless you control an Island or a Mountain.
{T}: Add {U} or {R}.

Heroic Reinforcements

Create two 1/1 white Soldier creature tokens. Until end of turn, creatures you control get +1/+1 and gain haste. (They can attack and {T} this turn.)

Plains

Island

Sacred Foundry

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

Rile

Rile deals 1 damage to target creature you control. That creature gains trample until end of turn.
Draw a card.

Feather, the Redeemed

Flying
Whenever you cast an instant or sorcery spell that targets a creature you control, exile that card instead of putting it into your graveyard as it resolves. If you do, return it to your hand at the beginning of the next end step.

Glacial Fortress

Glacial Fortress enters tapped unless you control a Plains or an Island.
{T}: Add {W} or {U}.

Aurelia, Exemplar of Justice

Flying
Mentor (Whenever this creature attacks, put a +1/+1 counter on target attacking creature with lesser power.)
At the beginning of combat on your turn, choose up to one target creature you control. Until end of turn, that creature gets +2/+0, gains trample if it's red, and gains vigilance if it's white.

Sheltering Light

Target creature gains indestructible until end of turn. Scry 1. (Damage and effects that say "destroy" don't destroy the creature.)

Hallowed Fountain

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

Samut's Sprint

Target creature gets +2/+1 and gains haste until end of turn. Scry 1.

Tenth District Legionnaire

Haste
Whenever you cast a spell that targets Tenth District Legionnaire, put a +1/+1 counter on Tenth District Legionnaire, then scry 1.

Clifftop Retreat

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

Beamsplitter Mage

Whenever you cast an instant or sorcery spell that targets only Beamsplitter Mage, if you control one or more other creatures that spell could target, choose one of those creatures. Copy that spell. The copy targets the chosen creature.

Stealth Mission

Put two +1/+1 counters on target creature you control. That creature can't be blocked this turn.