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.

Mines of Moria

Mines of Moria enters tapped unless you control a legendary creature.
{T}: Add {R}.
{3}{R}, {T}, Exile three cards from your graveyard: Create two Treasure tokens.

Swiftfoot Boots

Equipped creature has hexproof and haste. (It can't be the target of spells or abilities your opponents control. It can attack and {T} no matter when it came under your control.)
Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)

Treasure Vault

{T}: Add {C}.
{X}{X}, {T}, Sacrifice this land: Create X Treasure tokens.

Arena of Glory

This land enters tapped unless you control a Mountain.
{T}: Add {R}.
{R}, {T}, Exert this land: Add {R}{R}. If that mana is spent on a creature spell, it gains haste until end of turn. (An exerted permanent won't untap during your next untap step.)

Professional Face-Breaker

Menace
Whenever one or more creatures you control deal combat damage to a player, create a Treasure token.
Sacrifice a Treasure: Exile the top card of your library. You may play that card this turn.

Captain's Hook

Equipped creature gets +2/+0, has menace, and is a Pirate in addition to its other creature types.
Whenever this Equipment becomes unattached from a permanent, destroy that permanent.
Equip {1}

Blackblade Reforged

Equipped creature gets +1/+1 for each land you control.
Equip legendary creature {3}
Equip {7}

The Mary Janes

This spell costs {1} less to cast for each creature that attacked this turn.
Menace (This creature can't be blocked except by two or more creatures.)

Book of Mazarbul

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I — Amass Orcs 1. (Put a +1/+1 counter on an Army you control. It's also an Orc. If you don't control an Army, create a 0/0 black Orc Army creature token first.)
II — Amass Orcs 2.
III — Creatures you control get +1/+0 and gain menace until end of turn.

Blasphemous Act

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

Mountain

Kari Zev, Skyship Raider

First strike, menace
Whenever Kari Zev attacks, create Ragavan, a legendary 2/1 red Monkey creature token. Ragavan enters tapped and attacking. Exile that token at end of combat.

Choco-Comet

Choco-Comet deals X damage to any target.
Create a 2/2 green Bird creature token with "Whenever a land you control enters, this token gets +1/+0 until end of turn."

Abrade

Choose one —
• Abrade deals 3 damage to target creature.
• Destroy target artifact.

Kessig Wolfrider

Menace
{2}{R}, {T}, Exile three cards from your graveyard: Create a 3/2 red Wolf creature token.

Unexpected Windfall

As an additional cost to cast this spell, discard a card.
Draw two cards and create two Treasure tokens. (They're artifacts with "{T}, Sacrifice this token: Add one mana of any color.")

Doc Ock's Tentacles

Whenever a creature you control with mana value 5 or greater enters, you may attach this Equipment to it.
Equipped creature gets +4/+4.
Equip {5}

Wisecrack

Target creature deals damage equal to its power to itself. If that creature is attacking, Wisecrack deals 2 damage to that creature's controller.

Maximum Carnage

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I — Until your next turn, each creature attacks each combat if able and attacks a player other than you if able.
II — Add {R}{R}{R}.
III — This Saga deals 5 damage to each opponent.

Basalt Monolith

This artifact doesn't untap during your untap step.
{T}: Add {C}{C}{C}.
{3}: Untap this artifact.

Comet Storm

Multikicker {1} (You may pay an additional {1} any number of times as you cast this spell.)
Choose any target, then choose another target for each time this spell was kicked. Comet Storm deals X damage to each of them.

J. Jonah Jameson

When J. Jonah Jameson enters, suspect up to one target creature. (A suspected creature has menace and can't block.)
Whenever a creature you control with menace attacks, create a Treasure token.

Hammer of Purphoros

Creatures you control have haste.
{2}{R}, {T}, Sacrifice a land: Create a 3/3 colorless Golem enchantment artifact creature token.

Lightning Bolt

Lightning Bolt deals 3 damage to any target.

Bitterthorn, Nissa's Animus

Living weapon (When this Equipment enters, create a 0/0 black Phyrexian Germ creature token, then attach this to it.)
Equipped creature gets +1/+1.
Whenever equipped creature attacks, you may search your library for a basic land card, put it onto the battlefield tapped, then shuffle.
Equip {3}

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.

Interdimensional Web Watch

When this artifact enters, exile the top two cards of your library. Until the end of your next turn, you may play those cards.
{T}: Add two mana in any combination of colors. Spend this mana only to cast spells from exile.

Star Athlete

Menace
Whenever this creature attacks, choose up to one target nonland permanent. Its controller may sacrifice it. If they don't, this creature deals 5 damage to that player.
Blitz {3}{R} (If you cast this spell for its blitz cost, it gains haste and "When this creature dies, draw a card." Sacrifice it at the beginning of the next end step.)

Broadside Bombardiers

Menace, haste
Boast — Sacrifice another creature or artifact: This creature deals damage equal to 2 plus the sacrificed permanent's mana value to any target. (Activate only if this creature attacked this turn and only once each turn.)

Breaking of the Fellowship

Target creature an opponent controls deals damage equal to its power to another target creature that player controls. The Ring tempts you.

Lightning, Security Sergeant

Menace (This creature can't be blocked except by two or more creatures.)
Whenever Lightning deals combat damage to a player, exile the top card of your library. You may play that card for as long as you control Lightning.

Burnout Bashtronaut

Menace
Start your engines! (If you have no speed, it starts at 1. It increases once on each of your turns when an opponent loses life. Max speed is 4.)
{2}: This creature gets +1/+0 until end of turn.
Max speed — This creature has double strike.

Big Score

Edgewall Pack

Menace (This creature can't be blocked except by two or more creatures.)
When this creature enters, create a 1/1 black Rat creature token with "This token can't block."

Nykthos, Shrine to Nyx

{T}: Add {C}.
{2}, {T}: Choose a color. Add an amount of mana of that color equal to your devotion to that color. (Your devotion to a color is the number of mana symbols of that color in the mana costs of permanents you control.)

Academy Manufactor

If you would create a Clue, Food, or Treasure token, instead create one of each.

Chaos Warp

The owner of target permanent shuffles it into their library, then reveals the top card of their library. If it's a permanent card, they put it onto the battlefield.

Courageous Goblin

Whenever this creature attacks while you control a creature with power 4 or greater, this creature gets +1/+0 and gains menace until end of turn. (It can't be blocked except by two or more creatures.)

Valakut, the Molten Pinnacle

This land enters tapped.
Whenever a Mountain you control enters, if you control at least five other Mountains, you may have this land deal 3 damage to any target.
{T}: Add {R}.

Alpha Brawl

Target creature an opponent controls deals damage equal to its power to each other creature that player controls, then each of those creatures deals damage equal to its power to that creature.

Daily Bugle Building

{T}: Add {C}.
{1}, {T}: Add one mana of any color.
Smear Campaign — {1}, {T}: Target legendary creature gains menace until end of turn. Activate only as a sorcery.

Generous Plunderer

Menace
At the beginning of your upkeep, you may create a Treasure token. When you do, target opponent creates a tapped Treasure token.
Whenever this creature attacks, it deals damage to defending player equal to the number of artifacts they control.

Avalanche of Sector 7

Menace
Avalanche of Sector 7's power is equal to the number of artifacts your opponents control.
Whenever an opponent activates an ability of an artifact they control, Avalanche of Sector 7 deals 1 damage to that player.

Spider-Suit

Equipped creature gets +2/+2 and is a Spider Hero in addition to its other types.
Equip {3} ({3}: Attach to target creature you control. Equip only as a sorcery.)

Battlesong Berserker

Whenever you attack, target creature you control gets +1/+0 and gains menace until end of turn. (It can't be blocked except by two or more creatures.)

Bolt of Keranos

Bolt of Keranos deals 3 damage to any target. Scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Breeches, Brazen Plunderer

Menace
Whenever one or more Pirates you control deal damage to your opponents, exile the top card of each of those opponents' libraries. You may play those cards this turn, and you may spend mana as though it were mana of any color to cast those spells.
Partner (You can have two commanders if both have partner.)

Banefire

Banefire deals X damage to any target.
If X is 5 or more, this spell can't be countered and the damage can't be prevented.

Homeward Path

{T}: Add {C}.
{T}: Each player gains control of all creatures they own.

Sol Ring

Double Trouble

Double the power of each creature you control until end of turn.

Full Throttle

After this main phase, there are two additional combat phases.
At the beginning of each combat this turn, untap all creatures that attacked this turn.

Ghost-Spider, Gwen Stacy

Menace (This creature can't be blocked except by two or more creatures.)
Whenever Ghost-Spider attacks, she deals X damage to defending player, where X is the number of attacking creatures.

Alhammarret's Archive

If you would gain life, you gain twice that much life instead.
If you would draw a card except the first one you draw in each of your draw steps, draw two cards instead.

Veronica, Dissident Scribe

Menace
Whenever Veronica attacks, you may discard a card. If you do, draw a card.
Whenever you discard one or more nonland cards for the first time each turn, create a Junk token. (It's an artifact with "{T}, Sacrifice this token: Exile the top card of your library. You may play that card this turn. Activate only as a sorcery.")

Shock

Path of Ancestry

This land enters tapped.
{T}: Add one mana of any color in your commander's color identity. When that mana is spent to cast a creature spell that shares a creature type with your commander, scry 1. (Look at the top card of your library. You may put that card on the bottom.)

Assault on Osgiliath

Amass Orcs X, then Goblins and Orcs you control gain double strike and haste until end of turn. (To amass Orcs X, put X +1/+1 counters on an Army you control. It's also an Orc. If you don't control an Army, create a 0/0 black Orc Army creature token first.)

Arcane Signet

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

Breath of Fire

Breath of Fire deals 2 damage to target creature.

Rogue's Passage

{T}: Add {C}.
{4}, {T}: Target creature can't be blocked this turn.

Pain Distributor

Menace
Whenever a player casts their first spell each turn, they create a Treasure token.
Whenever an artifact an opponent controls is put into a graveyard from the battlefield, this creature deals 1 damage to that player.

Amulet of Vigor

Whenever a permanent you control enters tapped, untap it.

Ruby Medallion

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

Chandra's Ignition

Target creature you control deals damage equal to its power to each other creature and each opponent.

Blightsteel Colossus

Trample, infect, indestructible
If Blightsteel Colossus would be put into a graveyard from anywhere, reveal Blightsteel Colossus and shuffle it into its owner's library instead.

Rampaging Ferocidon

Menace
Players can't gain life.
Whenever another creature enters, this creature deals 1 damage to that creature's controller.

Chitinous Cloak

Equipped creature gets +2/+2 and has menace. (It can't be blocked except by two or more creatures.)
Equip {3}

The Fire Crystal

Red spells you cast cost {1} less to cast.
Creatures you control have haste.
{4}{R}{R}, {T}: Create a token that's a copy of target creature you control. Sacrifice it at the beginning of the next end step.

Mage Siege

Create a 0/1 black Wizard creature token with "Whenever you cast a noncreature spell, this token deals 1 damage to each opponent."