Best Polymorph Forms For Each Level?

[SleepIncarnate]

So, I'm curious as to what forms you all think are the best ones to turn party members into via polymorph for each level. Since the spell only allows you to turn them into beasts of CR equal to or lower than their level, that means we can't do the infamous t-rex right away when getting the spell at level 7, which is what started this thought process. I think the best one at CR 7 would probably be giant ape, but what about other levels? Does it seriously just cap out at t-rex at CR 8? What about casting the spell at 11th level?

Has anyone taken the time to look at this in the same kind of depth as moon druids look at all beasts they can become at each CR up to 6 when they hit level 18?

[JackPhoenix]

Giant Ape is the only CR 7 beast. Then there's T. Rex (and giant crab from TftYP) at CR 8. There are no higher-CR beasts.

[No brains]

Volo's Guide to Monsters gives some more dinosaurs. Quezalcouatl (not to be confused with couatl) is huge, has reach, and can fly all at cr 2. Around cr7 is a brontosaurus, which is one of the few options for becoming gargantuan.

[nickl_2000]

There aren't a lot of choices by RAW but if you are allowed there are so amazing choices in the creature codex and tome of beasts made by kobold press

[MaxWilson]

Declare an action like "I cast Polymorph to turn into a colossal Porcupine!" and see how your DM responds. Only your DM can truly tell you if there are beasts bigger than a Giant Ape, same as how only your DM can tell you if T Rexes are a thing.

[ImproperJustice]

I will say that Giant Ape with his intelligence of 7, and big hands allows for the wielding of magic items and Giant sized melee weapons if that sounds appealing....

[MeimuHakurei]

Here's a few good ones below CR 7:

-Giant Shark

Mainly useful for the swim speed and Blindsight. There's also the fact you have a +5 Con Mod, which makes it ever so slightly harder to break concentration if you use it on yourself. Blood Frenzy is nice to have as well.

-Giant Crocodile

Unlike the Giant Shark, this one's capable of going on land and has nice battlefield control riders on its multiattack options. Substantially lower hit points compared to the shark, however.

-Hulking Crab

Pretty nifty. Much higher AC than most beast forms, can Camouflage, also gets Blindsight and has two natural weapons to grapple and restrain with. Somewhat slow however.

-Giant Scorpion

A very niche pick due to its comparatively low HP. Mainly for poison damage (hits past lycanthrope immunities mainly) and a land-based Blindsight form.

-Rat

This form may be employed for scouting, but the main draw is that having a pathetic single attack, no special movement modes and abysmal Strength makes it the ideal form to transform opponents into.

-Quetzalcoatlus

It can fly but that's about the only thing it has to compete with the other options.

[EKruze]

If you're playing in Adventurer's League then Beasts of the Jungle Rot on DMs guild is a legal resource which offers some options of Titanosaurus (Gargantuan, CR7), Mosasaurus (Gargantuan, Swim 50, CR 8), and the Giganotosaurus (Gargantuan, Legendary Actions CR10) among other dinosaurs.

[ATHATH]

-Rat

This form may be employed for scouting, but the main draw is that having a pathetic single attack, no special movement modes and abysmal Strength makes it the ideal form to transform opponents into.
I personally prefer turning people into giant fire beetles, as they have a -2 WIS modifier. If you want to physically contain someone instead of mind-controlling them with Dominate Beast (cast by your Druid friend) and then dismissing the Polymorph to return them to their normal form (while still dominated), I can see the value of the rat.

I prefer turning myself into a cranium rat (or something that can fly, if we're using Polymorph and not a low-level Wild Shape) for scouting purposes, since they have telepathy and an immunity to all divination spells, thought-reading effects, and emotion-sensing effects.

Deep rothes can cast Dancing Lights at-will without requiring material components.

Apes and giant apes have ranged attacks.

Tressyms can detect poison and invisibility/invisible things and can fly.

Crag cats have Magic Resistance and can reflect/turn spells that target only themselves of 7th level or lower that they successfully save against back at/on their caster(s). They also have a permanent/innate Nondetection effect on themselves.

[NorthernPhoenix]

I like Giant Ape/Giant Eagle since they are both good for their purposes, and, critically, vastly more intelligent than most options

[No brains]

-Hulking Crab

Pretty nifty. Much higher AC than most beast forms, can Camouflage, also gets Blindsight and has two natural weapons to grapple and restrain with. Somewhat slow however.

-Quetzalcoatlus

It can fly but that's about the only thing it has to compete with the other options.

What is hulking crab from? I don't think I have that book.

In defense of Quetzalcoatlus from Volo's Guide to Monsters, it can fly at 80ft, is huge, has 10ft reach, flyby, and dive attack. It does have puny hp and ac, but if you can catch anything that only has 5-foot reach outside, you can strafe it with 6d6 beak attacks. Also being only at cr2, it makes a good polymorph pick for Greater Steeds or other allies who can used for area control.

Also a huge creature with only a 15 strength can still fly with up to 900 lbs of stuff. If you ever need to steal a whole vehicle, you can load up GTA: Late Cretaceous.

So while it's not going to win a straight fight, it's got talents that synergize with the wacky imagination a person with polymorph should have.