Polymorph decks transform small or expendable creatures into enormous threats by destroying, sacrificing, or replacing them with creatures from the library. They usually play very few creature cards so the outcome is pretty predictable.
Token generators provide safe targets without contaminating the creature pool, allowing effects such as Transmogrify to reliably find Atraxa, Grand Unifier, Emrakul, the Aeons Torn, or another suitably wild creature.
