[RPG] Does polymorph use a PC’s CR or its level

dnd-5epolymorphspells

I was discussing the spell with my DM relating to this question Can a Wizard polymorph low-level PCs into over-powered beasts? about the polymorph spell.

According to Polymorph's description,

The new form can be any beast whose challenge rating is equal to or
less than the target’s (or the target’s level, if it doesn't have a
challenge rating).

I was excited about the idea to turn one of my fellow group members into a giant ape or T-rex, but my DM told me that anyway with our current level (lvl 9) I would only be able to turn them into a CR 4 monster.
He bases his judgment on this part:

The new form can be any beast whose challenge rating is equal to or less than the target’s

From my understanding, PC's don't have a CR – CR seems to have been invented to adapt monsters' levels to players' levels (originally in D&D 3e). In other case, we could have just put experience levels to monsters instead of creating an alternate ranking system. And why does the spell specify:

(or the target’s level, if it doesn't have a challenge rating).

I'm still relatively new in D&D 5e world so I'm maybe wrong. I understand that at the end of the day the DM's word is law and I got no problem with that. But I was wondering if there was any precision points in the rules that I could show him if it's just a problem of interpretation?

I think that my DM isn’t making a house rule on purpose and is just misunderstanding the rules. I think he used a "conversion array" that he found on google: something like a level X creature is a normal threat for 4 level X PCs. Right now he tells me that he is right and the spell is just badly written.

So the question is does a PC fall under the

The new form can be any beast whose challenge rating is equal to or less than the target’s

part of the spell's rule or under the

(or the target’s level, if it doesn't have a challenge rating).

part of the spell's rule? Please justify.

Best Answer

Your DM has chosen to vary from the RAW

You correctly point out that by the letter of the rules, his ruling does not match the rules text for the polymorph spell.

The spell as written uses the character's level as the basis for the CR of the beast that the PC is polymorphed into.

The new form can be any beast whose challenge rating is equal to or less than the target’s (or the target’s level, if it doesn't have a challenge rating). (spell description, SRD p. 169)

The bolded part is the key.

You are also correct in understanding that the DM's ruling is how the game is played at his table. Now that you know what the ruling is, you know how powerful polymorph is in your DM's world.

What do I do?

I'd suggest that you discuss with your DM why he feels that the bolded part (above) of the spell text should not apply to a PC being polymorphed. Find out if a "balance1" motive is the case, or if it's a simple misunderstanding.

I'd further recommend you do this away from the table (not during a game session) and work with your DM to discover the process he goes through to determine the CR level of the PC under a polymorph spell. There is a section in the DMG (pages 273-285) that addresses how to build a monster or NPC and assign a CR to it. The DM may feel that the spell should work a different way, or, he may be using an unofficial "conversion array" as you mentioned in a comment, or this may be a simple misunderstanding. The DMG and the game's developers point out that the rules serve the game at the table, and the that DM is Master of Rules(DMG p. 5) so for the moment play within his guidance until that is revised (if it is revised).

Beyond that discussion, and finding out if the DM agrees on the rules text and makes a change, what you can do is:

  1. Check with the DM ahead of time on what the estimated CR is of a PC so that you know what you can try and polmorph them into.
  2. Play and have fun.

1 As an aside:
There is a school of thought that I have seen among various players and DMs in on-line discussions; they have fallen into the "polymorph is overpowered" school of thought. Those folks see a CR adjustment as a remedy to a perceived imbalance or loophole in the game. DM's do things like that for a wide variety of reasons with the intent of making the game play more smoothely/better at their table.