Is it possible to use a reaction from your class when your polymorphed form is reduced to 0 hit points and the excess carries over to you?
For example, let's say you're playing a rogue and your friendly wizard polymorphs you into a giant ape. Battles continues, and after a failed dexterity saving throw, you take 50 damage. Since your giant ape only had 10 hp left, you take 40 hp to your rogue health. Since you're not under the Polymorph spell, can you use your reaction to do Uncanny Dodge and only take half of the 40 damage you're taking?