Zinnia, Valley's Voice | Appa, Steadfast Guardian | Burning-Tree Emissary (and one other card)

Cards

Appa and
Burning-Tree Emissary in hand.
Zinnia and
Kaya on the battlefield (
Kaya with two or more loyalty counters on it).

Cast
Burning-Tree Emissary by paying its mana cost plus an additional ({2} magic symbol) for its offspring cost.
When
Burning-Tree Emissary enters, its innate ability and its offspring ability trigger.
Resolve the innate
Burning-Tree Emissary trigger, adding ({R} magic symbol) ({R} magic symbol) ({R} magic symbol) .
Resolve the offspring trigger, creating two token copies of
Burning-Tree Emissary that are 1/1.
When the
Burning-Tree Emissary tokens enter, they each trigger, adding six ({R} magic symbol) .
Cast
Appa by paying its mana cost plus an additional ({2} magic symbol) for its offspring cost.
When
Appa enters, its innate ability and its offspring ability trigger.
Resolve the innate
Appa trigger, airbending the nontoken
Burning-Tree Emissary.
Resolve the offspring trigger, creating two token copies of
Appa that are 1/1.
Put both
Appa tokens into your graveyard due to the legend rule.
Both
Appa tokens' enter-the-battlefield ability trigger, airbending
Appa with one trigger and nothing with the other.
Cast
Burning-Tree Emissary from exile by paying ({2} magic symbol) plus an additional ({2} magic symbol) for its offspring cost.
Repeat steps 2 through 5 once.
Cast
Appa from exile by paying ({2} magic symbol) plus an additional ({2} magic symbol) for its offspring cost.
Repeat from step 7.

Once you have extra mana, other nonland permanents can be airbended using
Appa and returned to the battlefield each loop as desired.

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