When Aang enters, airbend another target creature. (Exile it. While it's exiled, its owner may cast it for 2 rather than its mana cost.)
Whenever one or more creatures you control leave the battlefield without dying, you get an experience counter.
At the beginning of your upkeep, create a 1/1 white Ally creature token for each experience counter you have.

NOTE: Stock image, not actual card.