There is an exploit that, when used correctly, allows your Ditto to trick a wild Pokemon into using Transform.

This is only possible with the Pokemon Pidgey, Pidgeotto, Spearow, or Fearow as they are the only wild Pokemon who know Mirror Move. If your Ditto uses Transform on a wild Pokemon who uses Mirror Move in the same turn, The wild Pokemon transforms into Ditto. The game also registers the wild Pokemon as Ditto.
Contributed by AussieYak
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