Runaway Steam-Kin

Whenever you cast a red spell, if this creature has fewer than three +1/+1 counters on it, put a +1/+1 counter on this creature.
Remove three +1/+1 counters from this creature: Add {R}{R}{R}.

Electro, Assaulting Battery

Flying
You don't lose unspent red mana as steps and phases end.
Whenever you cast an instant or sorcery spell, add {R}.
When Electro leaves the battlefield, you may pay {X}. When you do, he deals X damage to target player.

Mountain

Gamble

Search your library for a card, put that card into your hand, discard a card at random, then shuffle.

Ashling, Flame Dancer

You don't lose unspent red mana as steps and phases end.
Magecraft — Whenever you cast or copy an instant or sorcery spell, discard a card, then draw a card. If this is the second time this ability has resolved this turn, Ashling deals 2 damage to each opponent and each creature they control. If it's the third time, add {R}{R}{R}{R}.

Blood Moon

Command Beacon

{T}: Add {C}.
{T}, Sacrifice this land: Put your commander into your hand from the command zone.

Wheel of Fortune

Each player discards their hand, then draws seven cards.

Dragon's Approach

Dragon's Approach deals 3 damage to each opponent. You may exile Dragon's Approach and four cards named Dragon's Approach from your graveyard. If you do, search your library for a Dragon creature card, put it onto the battlefield, then shuffle.
A deck can have any number of cards named Dragon's Approach.

Agate Assault

Choose one —
• Agate Assault deals 4 damage to target creature. If that creature would die this turn, exile it instead.
• Exile target artifact.

Temple of Power

(Transforms from Ojer Axonil, Deepest Might.)
{T}: Add {R}.
{2}{R}, {T}: Transform this land. Activate only if red sources you controlled dealt 4 or more noncombat damage this turn and only as a sorcery.

Ojer Axonil, Deepest Might

Trample
If a red source you control would deal an amount of noncombat damage less than Ojer Axonil's power to an opponent, that source deals damage equal to Ojer Axonil's power instead.
When Ojer Axonil dies, return it to the battlefield tapped and transformed under its owner's control.

Ojer Axonil, Deepest Might // Temple of Power

Faithless Looting

Draw two cards, then discard two cards.
Flashback {2}{R} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Fiery Inscription

When this enchantment enters, the Ring tempts you.
Whenever you cast an instant or sorcery spell, this enchantment deals 2 damage to each opponent.

Ancient Copper Dragon

Flying
Whenever this creature deals combat damage to a player, roll a d20. You create a number of Treasure tokens equal to the result.

Tecutlan, the Searing Rift

(Transforms from Brass's Tunnel-Grinder.)
{T}: Add {R}.
Whenever you cast a permanent spell using mana produced by Tecutlan, discover X, where X is that spell's mana value.

Brass's Tunnel-Grinder

When Brass's Tunnel-Grinder enters, discard any number of cards, then draw that many cards plus one.
At the beginning of your end step, if you descended this turn, put a bore counter on Brass's Tunnel-Grinder. Then if there are three or more bore counters on it, remove those counters and transform it. (You descended if a permanent card was put into your graveyard from anywhere.)

Brass's Tunnel-Grinder // Tecutlan, the Searing Rift

Sol Ring

Galvanic Relay

Exile the top card of your library. During your next turn, you may play that card.
Storm (When you cast this spell, copy it for each spell cast before it this turn.)

Extraplanar Lens

Imprint — When this artifact enters, you may exile target land you control.
Whenever a land with the same name as the exiled card is tapped for mana, its controller adds one mana of any type that land produced.

Underworld Breach

Each nonland card in your graveyard has escape. The escape cost is equal to the card's mana cost plus exile three other cards from your graveyard. (You may cast cards from your graveyard for their escape cost.)
At the beginning of the end step, sacrifice this enchantment.

The Great Work

(As this Saga enters and after your draw step, add a lore counter.)
I — This Saga deals 3 damage to target opponent and each creature they control.
II — Create three Treasure tokens.
III — Until end of turn, you may cast instant and sorcery spells from any graveyard. If a spell cast this way would be put into a graveyard, exile it instead. Exile this Saga, then return it to the battlefield (front face up).

Urabrask

First strike
Whenever you cast an instant or sorcery spell, Urabrask deals 1 damage to target opponent. Add {R}.
{R}: Exile Urabrask, then return it to the battlefield transformed under its owner's control. Activate only as a sorcery and only if you've cast three or more instant and/or sorcery spells this turn.

Urabrask // The Great Work

Guttersnipe

Whenever you cast an instant or sorcery spell, this creature deals 2 damage to each opponent.

Jeska's Will

Choose one. If you control a commander as you cast this spell, you may choose both instead.
• Add {R} for each card in target opponent's hand.
• Exile the top three cards of your library. You may play them this turn.

Deflecting Swat

If you control a commander, you may cast this spell without paying its mana cost.
You may choose new targets for target spell or ability.

Thran Dynamo

Reverberate

Copy target instant or sorcery spell. You may choose new targets for the copy.

Shinka, the Bloodsoaked Keep

{T}: Add {R}.
{R}, {T}: Target legendary creature gains first strike until end of turn.

Aggravated Assault

{3}{R}{R}: Untap all creatures you control. After this main phase, there is an additional combat phase followed by an additional main phase. Activate only as a sorcery.

Primal Wellspring

(Transforms from Primal Amulet.)
{T}: Add one mana of any color. When that mana is spent to cast an instant or sorcery spell, copy that spell and you may choose new targets for the copy.

Primal Amulet

Instant and sorcery spells you cast cost {1} less to cast.
Whenever you cast an instant or sorcery spell, put a charge counter on this artifact. Then if there are four or more charge counters on it, you may remove those counters and transform it.

Primal Amulet // Primal Wellspring

Cloud Key

As this artifact enters, choose artifact, creature, enchantment, instant, or sorcery.
Spells you cast of the chosen type cost {1} less to cast.

Mind Stone

{T}: Add {C}.
{1}, {T}, Sacrifice this artifact: Draw a card.

Arcane Signet

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

Twinflame Tyrant

Flying
If a source you control would deal damage to an opponent or a permanent an opponent controls, it deals double that damage instead.

Ancient Tomb

{T}: Add {C}{C}. This land deals 2 damage to you.

Terror of Mount Velus

Flying
Double strike (This creature deals both first-strike and regular combat damage.)
When this creature enters, creatures you control gain double strike until end of turn.

Neheb, the Eternal

Afflict 3 (Whenever this creature becomes blocked, defending player loses 3 life.)
At the beginning of each of your postcombat main phases, add {R} for each 1 life your opponents have lost this turn.

Blasphemous Act

This spell costs {1} less to cast for each creature on the battlefield.
Blasphemous Act deals 13 damage to each creature.

Ruby Medallion

Red spells you cast cost {1} less to cast.

Seething Song

Mizzix's Mastery

Exile target card that's an instant or sorcery from your graveyard. For each card exiled this way, copy it, and you may cast the copy without paying its mana cost. Exile Mizzix's Mastery.
Overload {5}{R}{R}{R} (You may cast this spell for its overload cost. If you do, change "target" in its text to "each.")

Jeska, Thrice Reborn

Jeska enters with a loyalty counter on her for each time you've cast a commander from the command zone this game.
0: Choose target creature. Until your next turn, if that creature would deal combat damage to one of your opponents, it deals triple that damage to that player instead.
−X: Jeska deals X damage to each of up to three targets.
Jeska, Thrice Reborn can be your commander.
Partner

Mana Geyser

Add {R} for each tapped land your opponents control.

Light Up the Stage

Spectacle {R} (You may cast this spell for its spectacle cost rather than its mana cost if an opponent lost life this turn.)
Exile the top two cards of your library. Until the end of your next turn, you may play those cards.

Wrenn's Resolve

Exile the top two cards of your library. Until the end of your next turn, you may play those cards.

Harnfel, Horn of Bounty

Discard a card: Exile the top two cards of your library. You may play those cards this turn.

Birgi, God of Storytelling

Whenever you cast a spell, add {R}. Until end of turn, you don't lose this mana as steps and phases end.
Creatures you control can boast twice during each of your turns rather than once.