The new form can be any beast whose (or target’s level, if it doesn’t have a challenge rating).
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But let’s look at the spell’s description: Polymorph – This spell transforms a creature that you can see within range into a new form.
When it reverts to its normal form, the creature returns to the number of hit points it had before it transformed.
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Polymorph is a 4th level transmutation spell that is usable by wizards, druids, and bards when they reach level 7.
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