Can someone explain why Mass Polymorph has the limitation of a beast you have seen, while this one does not?

Rules as has been clarified no. Evidently the 5e devs determine everything a character can do (including class abilities, spellcasting, etc) to be part of their game statistics. So if its not in the new forms stat block, you cant do it. 

What's your take on say if a vampire turned into a bat or wolf or even mist - would a divine sense detect him as undead or would the polymorph cover that up?

I wonder if you could polymorph a mouse into a Sperm Whale that weighs 90,000 lbs and use it as a bomb. Fly over enemy, polymorph and drop a creature the size of a dump truck on them. 

Fun fact: this spell doesn't say anything about who picks what the new form is.

Wizard: I cast Polymorph on the dragon

DM: He failed the save, what do you morph him into?

Wizard: A grin

DM: Oh, please no.

Wizard: A pickle

DM: Please no

Wizard: Pickle Rick

”The transformation lasts for the duration, or until the target drops to 0 hit points or dies.“

So could my PC hold concentration for the hour and pop in-and-out of the Polymorph form, or would dropping concentration be how a PC returns to humanoid form before the end of the hour?

(I’m 90% sure it’s the latter, but just want to make sure I’m understanding this correctly.)

HI guys,

let’s assume I polym. Into a T-Rex.

since Poly is a concentration spell, in case I take damage as a T-Rex should I make a successful constitution roll or the spell ends? (Meaning that I’ll switch back immediately in my standard form).

thx

If you disintegrate a polymorphed enemy, say you turned it into a mouse or something, how would that interact? Disintegrate reduces the target to dust if it's hit points reach zero and polymorph ends at the same time. How would the spell effects chain?

Quote from Anton9800 >>

If you disintegrate a polymorphed enemy, say you turned it into a mouse or something, how would that interact? Disintegrate reduces the target to dust if it's hit points reach zero and polymorph ends at the same time. How would the spell effects chain?

The target assumes the hit points of its new form. When it reverts to its normal form, the creature returns to the number of hit points it had before it transformed. If it reverts as a result of dropping to 0 hit points, any excess damage carries over to its normal form. As long as the excess damage doesn't reduce the creature's normal form to 0 hit points, it isn't knocked unconscious.

I assume that if the disintegrate damage carried over and reduced you to 0 HP as well, then you would turn to dust. If it just knocked you out of poly and carried over some damage, but not to 0, it wouldnt turn you to dust.

I used this once to transform our enemy into a box turtle then just picked him up and dropped him into a nearby lava pit.

Quote from NedyBonz >>

What happens if polymorph's target is in a space that will not accommodate the new form? For instance polymorphing another character into a T-Rex (huge beast) in a cramped 6 ft. by 6ft. tunnel?

I'd say it's like teleporting to an occupied space, you take bludgeoning damage and the spell fails.

does it mean beast as in the monster type?

Please please please add a page/table with all the creatures up to date with the latest books <3

Hmmm, so is there anything preventing me from using polymorph to transform a creature into a rat, and then use a hawk or owl Wild Companion to fly the rat up a few hundred  feet in the air and release it, and then as soon as it starts to fall I stop concentrating?   I'm thinking the creature resumes it's natural form more than 200 feet in the air so takes 20d6 fall damage?

I am doing an adventure where at the start my group is polymorphed into orcs how should i edit their sheets?

Just give them orc statblocks. It feels kind of mean to say "Oh, you made a character, well here's your orc statblock instead" though.

https://www.dndbeyond.com/monsters/orc

thanks that makes things easier 

Quote from Chewsock >>

I wonder if you could polymorph a mouse into a Sperm Whale that weighs 90,000 lbs and use it as a bomb. Fly over enemy, polymorph and drop a creature the size of a dump truck on them. 

 "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)."

So, no, you can't turn a mouse into a whale.  However, you could turn the whale into a mouse, then fly over the enemy, deal a hit point of damage on the mouse to make it revert, and drop a whale.

Quote from theferal >>

does it mean beast as in the monster type?

 

Yes, it absolutely does. As far as the *rules* are concerned, there is no other 'beast' in the game.