Declare Mardu Siegebreaker as an attacker, triggering its second ability, creating at least one token copy of Restoration Angel that is tapped and attacking.
When the Restoration Angel token(s) enter the battlefield, they trigger.
Resolve the first trigger, blinking Mardu Siegebreaker.
Mardu Siegebreaker leaves and enters the battlefield, causing the nontoken Restoration Angel to return to the battlefield from exile, and triggering Restoration Angel and Mardu Siegebreaker's first ability.
Resolve the Mardu Siegebreaker trigger, exiling the nontoken Restoration Angel until Mardu Siegebreaker leaves the battlefield.
Resolve the Restoration Angel trigger, blinking Mardu Siegebreaker.
Repeat from step 4.

Infinite LTB

Infinite ETB

Mardu Siegebreaker

Restoration Angel

Declare Mardu Siegebreaker as an attacker, triggering its second ability, creating a token copy of Port Razer that is tapped and attacking.
Deal combat damage with the Port Razer token, triggering its ability, untapping all creatures you control and causing you to get an additional combat phase after this one.
Repeat each combat phase.

Infinite combat phases

Infinite untap of creatures you control

Infinite mana creatures you control can produce

Infinite sacrifice triggers

Infinite death triggers

Infinite combat damage

Infinite tapped creature tokens

Port Razer

Declare Mardu Siegebreaker as an attacker, triggering its second ability, creating a token copy of Professional Face-Breaker that is tapped and attacking each opponent.
Deal combat damage with Mardu Siegebreaker and any number of Professional Face-Breaker token(s), triggering each Professional Face-Breaker, creating that many Treasure tokens.
Move to your postcombat main phase.
Activate up to five Treasures by tapping and sacrificing them, adding {R} for each Treasure sacrificed this way.
Activate Aggravated Assault by paying {3}{R}{R}, causing you to untap all creatures you control and to get an additional combat and main phase after this one.
Repeat.

Infinite colored mana

Infinite creature tokens

Infinite Treasure tokens

Professional Face-Breaker

Aggravated Assault

Declare Mardu Siegebreaker as an attacker, triggering its second ability, creating at least two token copies of Éomer that is tapped and attacking.
Put all but one Éomer token into your graveyard due to the legend rule.
When the Éomer token(s) die, you will get at least one Éomer trigger, causing you to untap all creatures you control and to get an additional combat phase after this one.
Repeat each combat phase.

Éomer, Marshal of Rohan

Activate Kiki-Jiki by tapping it, creating a token copy of Mardu Siegebreaker.
When the Mardu Siegebreaker token enters the battlefield, it triggers, exiling Kiki-Jiki until Mardu Siegebreaker leaves the battlefield.
Activate Goblin Bombardment by sacrificing the Mardu Siegebreaker token.
When the Mardu Siegebreaker token dies, Kiki-Jiki is returned from exile to the battlefield.
Resolve the Goblin Bombardment ability.
Repeat.

Infinite damage

Kiki-Jiki, Mirror Breaker

Goblin Bombardment

Cast Sister Hospitaller by paying {4}{W}{B}.
When Sister Hospitaller enters, it triggers, returning Mardu Siegebreaker from your graveyard to the battlefield and causing you to gain life equal to its mana value.
When Mardu Siegebreaker enters, it triggers, exiling Sister Hospitaller until Mardu Siegebreaker leaves the battlefield.
Activate Altar of Dementia by sacrificing Mardu Siegebreaker.
When Mardu Siegebreaker leaves the battlefield, Sister Hospitaller is returned from exile to the battlefield.
Repeat from step 2.
Resolve all Altar of Dementia abilities.

Infinite mill

Infinite self-mill

Infinite lifegain triggers

Infinite lifegain

Sister Hospitaller

Altar of Dementia

Declare Mardu Siegebreaker as an attacker, triggering its second ability, creating a token copy of Rose Room Treasurer tapped and attacking each opponent.
When the Rose Room Treasurer tokens enter the battlefield, they each trigger for each other token that entered the battlefield, and any other Rose Room Treasurer(s) you control trigger for each token that entered the battlefield.
Resolve a Rose Room Treasurer trigger, creating a Treasure token if its the first or second time that ability has resolved this turn, or choosing not to pay otherwise.
Repeat step 3 for each remaining trigger.
Move to your postcombat main phase.
Activate five Treasures by tapping and sacrificing them, adding {3}{R}{R}.
Activate Aggravated Assault by paying {3}{R}{R}, causing you to untap all creatures you control and to get an additional combat and main phase after this one.
Repeat.

Near-infinite ETB

Near-infinite LTB

Near-infinite death triggers

Near-infinite sacrifice triggers

Near-infinite colored mana

Near-infinite Treasure tokens

Near-infinite combat phases

Near-infinite untap of creatures you control

Near-infinite mana creatures you control can produce

Rose Room Treasurer

Cast Metamorphosis Fanatic by paying {4}{B}{B}.
When Metamorphosis Fanatic enters, it triggers, returning Mardu Siegebreaker from your graveyard to the battlefield.
When Mardu Siegebreaker enters, it triggers, exiling Metamorphosis Fanatic until Mardu Siegebreaker leaves the battlefield.
Activate Altar of Dementia by sacrificing Mardu Siegebreaker.
When Mardu Siegebreaker leaves the battlefield, Metamorphosis Fanatic is returned from exile to the battlefield.
Repeat from step 2.
Resolve all Altar of Dementia abilities.

Metamorphosis Fanatic

Cast Ruthless Technomancer by paying {3}{B}.
When Ruthless Technomancer enters the battlefield, it triggers, causing you to sacrifice Dargo and create seven Treasure artifact tokens.
Choose to return Dargo to the command zone from your graveyard.
Activate five Treasures by tapping and sacrificing them, adding {1}{R}{R}{W}{B}.
If you cannot currently cast Dargo for {R}, including commander tax, activate a Treasure by tapping and sacrificing it, adding one mana of any color. Repeat this until you can cast Dargo for {R} and/or you run out of Treasures.
Cast Dargo from the command zone by paying at most {R}.
Cast Mardu Siegebreaker by paying {1}{R}{W}{B}.
When Mardu Siegebreaker enters the battlefield, its first ability triggers, exiling Ruthless Technomancer until Mardu Siegebreaker leaves the battlefield.
Declare Mardu Siegebreaker as an attacker, triggering its second ability, creating a token copy of Ruthless Technomancer that is tapped and attacking.
When the Ruthless Technomancer token enters the battlefield, it triggers, causing you to sacrifice Mardu Siegebreaker and create four Treasure tokens.
When Mardu Siegebreaker leaves the battlefield, the nontoken Ruthless Technomancer returns to the battlefield from exile.
When the nontoken Ruthless Technomancer enters the battlefield, it triggers, causing you to sacrifice Dargo and create seven Treasure tokens.
Choose to return Dargo to the command zone from your graveyard.
Move to your postcombat main phase.
Activate four Treasures by tapping and sacrificing them, adding {2}{B}{R}.
Cast Dargo from the command zone by paying {R} and sacrificing the nontoken Ruthless Technomancer.
Activate the token Ruthless Technomancer by paying {2}{B} and sacrificing two Treasures, returning the nontoken Ruthless Technomancer from your graveyard to the battlefield.
Repeat from step 12, skipping step 14 as you are already in a main phase.

Combos with "Mardu Siegebreaker"