Jirina Kudro | Mana Echoes | Pitiless Plunderer (and one other card)

Cards

({1} magic symbol) ({R} magic symbol) ({W} magic symbol) ({B} magic symbol) plus enough mana to pay for commander tax, if applicable, or an additional ({R} magic symbol) , ({W} magic symbol) or ({B} magic symbol) if you haven't cast Jirina from the command zone this game available.

Cast Jirina from the command zone by paying ({1} magic symbol) ({R} magic symbol) ({W} magic symbol) ({B} magic symbol) plus commander tax, if applicable.
When Jirina enters the battlefield, it and
Mana Echoes trigger.
Resolve the Jirina trigger, creating a 1/1 Human Soldier creature token for each time you've cast Jirina from the command zone this game.
When the Human Soldiers enter the battlefield,
Mana Echoes triggers that many times.
Resolve the first
Mana Echoes trigger, adding ({C} magic symbol) for each Human and Soldier you control.
Repeat step 5 for each remaining
Mana Echoes trigger created in steps 2 and 4.
Activate
Yahenni twice by sacrificing Jirina and a Human Soldier.
Choose to return Jirina to the command zone from your graveyard.
When Jirina and the Human Soldier die,
Pitiless Plunderer triggers twice, creating two Treasure tokens.
Holding priority, if you control a Human Soldier, activate
Yahenni by sacrificing a Human Soldier.
If you sacrificed a Human Soldier this way,
Pitiless Plunderer triggers, creating a Treasure token.
Resolve the
Yahenni abilities from steps 7 and 10.
Activate up to three Treasures by tapping and sacrificing them, adding any combination of ({R} magic symbol) , ({W} magic symbol) and ({B} magic symbol) .
Repeat.

This combo has been estimated to be Exhibition (Bracket 1+).