Can you polymorph a dead creature? If so, would the wounds sustained by the target's original form appear on the polymorphed form?
A possible scenario would be you're hunting a stag on the king's grounds, and when the sheriff says "You're in big trouble, mister", you can say "Oh no, this, this is just a weevil. Nothing to worry about."
From the PHB 266:
The transformation lasts for the duration, or until the target drops to 0 hit points or dies.
The wording of the spell is important, because it specifically says 'the target'. You are targeting the original, dead creature, so once your target (the dead creature) drops to 0 hit points or dies, they revert. However, since they are already at 0 hit points or dead, the spell would necessarily fail immediately. At best, it would hit the creature and immediately fail. More than likely, you wouldn't even be able to target the dead creature, as whatever mechanism the spell uses to choose and sustain itself on a target appears to rely on the target's being alive and conscious the entire time.
No
This spell transforms a creature that you can see within range into a new form.
A dead creature is not a creature. It is an object in the parlance of D&D and would be subject to spells that affect objects.
Consider the wording of Animate Dead:
Choose a pile of bones or a corpse of a Medium or Small humanoid within range. Your spell imbues the target with a foul mimicry of life, raising it as an undead creature.
Before: not a creature, After: creature.
and Animate Objects:
Choose up to ten nonmagical objects within range that are not being worn or carried. ... Each target animates and becomes a creature ...
Before: not a creature, After: creature.
So, you could animate it, making it a creature, and then polymorph it.
This is answer by the PHB Errata:
Polymorph (p. 266). This spell can’t affect a target that has 0 hit points.
Dead things tend to have 0 HP so no, you can't use Polymorph on something that is dead.
You can cast True Polymorph on a dead thing.
True Polymorph explicitly operates on objects (PHB p.283). Per “Is a dead creature's body considered an "object"?”, corpses are objects. So you can little-p polymorph a corpse even though you cannot cast big-p Polymorph, the 4th level spell, on it. You may not be able to True Polymorph a corpse into another corpse since the spell does not explicitly allow the case of object-to-object transformation. Disallowing it seems illogical to me, but it might be disallowed.
It's worth noting, or it amuses me to note at least, that objects also have hit points (DMG p.247). A corpse therefore has a non-zero number of HP :P
As to whether the resultant form can have any wounds: I don't know but not by default. True Polymorph doesn't seem to indicate control over fine detail, but it doesn't deny it either. Since new creature forms have full HP, I'd say that without specifying that you're polymorphing a corpse with gashes into another corpse with gashes, and having that be allowed in the first place, you'd wind up with something intact.
Based on this:
The transformation lasts for the duration, or until the target drops to 0 hit points or dies.
It would seem that a dead entity isn't a valid target, since as soon as something dies the magic wears off. I would think that if it's already dead it can't hold the magic either.
