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

Zariel, Archduke of Avernus

+1: Creatures you control get +1/+0 and gain haste until end of turn.
0: Create a 1/1 red Devil creature token with "When this token dies, it deals 1 damage to any target."
−6: You get an emblem with "At the end of the first combat phase on your turn, untap target creature you control. After this phase, there is an additional combat phase."

Hellkite Charger

Flying, haste
Whenever this creature attacks, you may pay {5}{R}{R}. If you do, untap all attacking creatures and after this phase, there is an additional combat phase.

Savage Beating

Cast this spell only during combat on your turn.
Choose one —
• Creatures you control gain double strike until end of turn.
• Untap all creatures you control. After this phase, there is an additional combat phase.
Entwine {1}{R} (Choose both if you pay the entwine cost.)

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.

Breath of Fury

Enchant creature you control
When enchanted creature deals combat damage to a player, sacrifice it and attach this Aura to a creature you control. If you do, untap all creatures you control and after this phase, there is an additional combat phase.

Éomer, Marshal of Rohan

Haste
Whenever one or more other attacking legendary creatures you control die, untap all creatures you control. After this phase, there is an additional combat phase. This ability triggers only once each turn.

Seize the Day

Untap target creature. After this main phase, there is an additional combat phase followed by an additional main phase.
Flashback {2}{R} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Karlach, Fury of Avernus

Whenever you attack, if it's the first combat phase of the turn, untap all attacking creatures. They gain first strike until end of turn. After this phase, there is an additional combat phase.
Choose a Background (You can have a Background as a second commander.)

Bloodghast

This creature can't block.
This creature has haste as long as an opponent has 10 or less life.
Landfall — Whenever a land you control enters, you may return this card from your graveyard to the battlefield.

Combat Celebrant

If this creature hasn't been exerted this turn, you may exert it as it attacks. When you do, untap all other creatures you control and after this phase, there is an additional combat phase. (An exerted creature won't untap during your next untap step.)

Muraganda Raceway

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.)
{T}: Add {C}.
Max speed — {T}: Add {C}{C}.

Fear of Missing Out

When this creature enters, discard a card, then draw a card.
Delirium — Whenever this creature attacks for the first time each turn, if there are four or more card types among cards in your graveyard, untap target creature. After this phase, there is an additional combat phase.

Great Train Heist

Spree (Choose one or more additional costs.)
+ {2}{R} — Untap all creatures you control. If it's your combat phase, there is an additional combat phase after this phase.
+ {2} — Creatures you control get +1/+0 and gain first strike until end of turn.
+ {R} — Choose target opponent. Whenever a creature you control deals combat damage to that player this turn, create a tapped Treasure token.

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.

Ormendahl, Profane Prince

Westvale Abbey

{T}: Add {C}.
{5}, {T}, Pay 1 life: Create a 1/1 white and black Human Cleric creature token.
{5}, {T}, Sacrifice five creatures: Transform this land, then untap it.

Westvale Abbey // Ormendahl, Profane Prince

Coalstoke Gearhulk

Menace, deathtouch
When this creature enters, put target creature card with mana value 4 or less from a graveyard onto the battlefield under your control with a finality counter on it. That creature gains menace, deathtouch, and haste. At the beginning of your next end step, exile that creature.

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.

Grim Reaper's Sprint

Morbid — This spell costs {3} less to cast if a creature died this turn.
Enchant creature
When this Aura enters, untap each creature you control. If it's your main phase, there is an additional combat phase after this phase.
Enchanted creature gets +2/+2 and has haste.

Relentless Assault

Untap all creatures that attacked this turn. After this main phase, there is an additional combat phase followed by an additional main phase.

Isengard Unleashed

Damage can't be prevented this turn. If a source you control would deal damage this turn to an opponent or a permanent an opponent controls, it deals triple that damage instead.
Flashback {4}{R}{R}{R} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Draconautics Engineer

Exhaust — {R}: Other creatures you control gain haste until end of turn. Put a +1/+1 counter on this creature. (Activate each exhaust ability only once.)
Exhaust — {3}{R}: Create a 4/4 red Dinosaur Dragon creature token with flying.

Fiery Emancipation

If a source you control would deal damage to a permanent or player, it deals triple that damage to that permanent or player instead.

The Aetherspark

As long as The Aetherspark is attached to a creature, The Aetherspark can't be attacked and has "Whenever equipped creature deals combat damage during your turn, put that many loyalty counters on The Aetherspark."
+1: Attach The Aetherspark to up to one target creature you control. Put a +1/+1 counter on that creature.
−5: Draw two cards.
−10: Add ten mana of any one color.

Akki Battle Squad

Whenever one or more modified creatures you control attack, untap all modified creatures you control. After this phase, there is an additional combat phase. This ability triggers only once each turn. (Equipment, Auras you control, and counters are modifications.)