Stangg, Echo Warrior + Éomer, Marshal of Rohan + Rionya, Fire Dancer Combo

All permanents on the battlefield.

Stangg does not have summoning sickness. An opponent cannot block and kill Stangg. You control another legendary creature that can attack this turn. You have a way to kill the additional legendary creature at instant speed.

At the beginning of your combat phase, Rionya triggers, creating at least one token copy of Éomer with haste.

Put all but the newest Éomer into your graveyard due to the legend rule.

Declare Stangg and the additional legendary creature as attackers.

Stangg triggers, creating a 3/4 Stangg Twin creature token that is tapped and attacking.

Holding priority, kill the additional legendary creature.

When the creature dies, the Éomer token triggers, causing you to untap all creatures you control and to get at least one additional combat phase after this one.

Move to your next combat phase.

At the beginning of your combat phase, Rionya triggers, creating at least one token copy of Éomer with haste.

Put all but the newest Éomer into your graveyard due to the legend rule.

Declare Stangg as an attacker.

Stangg triggers, creating a 3/4 Stangg Twin creature token that is tapped and attacking.

Put either Stangg Twin token into your graveyard due to the legend rule.

Repeat from step 6.

Infinite combat phases

Infinite death triggers

Infinite creature ETB

Infinite creature LTB

Infinite mana creatures you control can produce

Infinite untap of creatures you control