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When Burdened Aerialist enters the battlefield, create a Treasure token. (It's an artifact with "{T}, Sacrifice this artifact: Add one mana of any color.")
Whenever you sacrifice a token, Burdened Aerialist gains flying until end of turn.
Burdened Aerialist's ability will trigger whenever you sacrifice a token for any reason, not just when you sacrifice Treasure tokens.
If a blocked creature gains flying after blockers are declared, it won't cause that creature to become unblocked, even if the blocking creature doesn't have flying or reach.
