@JeremyECrawford One of my player is using polymorph at himself to be a TyrannosaurusRex.Isnt he abusing?Is that the intention of the spell?
— Enrique Delgado Torr (@enrikisinger) February 27, 2016
You can cast polymorph on yourself, provided you can see yourself. #DnD https://t.co/MQ0FzPkrYX
— Jeremy Crawford (@JeremyECrawford) February 27, 2016
@JeremyECrawford You can always see your hand, for example, Do you mean you need to see the whole body in order the spell to work?
— Enrique Delgado Torr (@enrikisinger) February 27, 2016
To see yourself, just look down. Something like blindness or darkness can prevent it. #DnD https://t.co/gfyXUwMhhi
— Jeremy Crawford (@JeremyECrawford) March 1, 2016
are they even in the MM
Yes theres a small section of dinosaurs in the MM. Shoot, tomb of annihilation had them as part of the campaign!
Sounds like metagaming. Have the character ever seen a T-rex? If not, how can he even get that idea?
I would restrict it to beasts that the player has seen or at least has knowledge about – in game or in the characters past.
The play is, presumably, a well-read and learned studier of all the wonders the world has to offer. Are you really going to force a player to sit down and roleplay out each and every individual creature they’ve seen in their entire lives? Just let the player do something cool. There’s very little to be gained from micromanaging what a character knows about their own abilities.
Let me ask you this: Do you also accuse the Fighter of metagaming when he wants to use Disarming Strike on the enemy swordsman? After all, maybe he’s never seen a War Pick or a Glaive before. Do you micromanage all classes’ abilities, or just spellcasters?
Have YOU ever actually seen ba T-Rex?
Restricting it to beasts already seen is nerfing the spell, as it includes no such stipulation. Contrast to Wlid Shape, which does. The difference is deliberate.
I just think of it as the character imagining the beast if they haven’t seen it before. Maybe it’s not exactly like the drawing in the MM, but it’s the CR that matters. As long as you are holding to that restriction, it’s balanced. It’s easy enough to come up with an explanation that lets the player cast the spell as written, if you’re interested in letting players make full use of their abilities, which is generally an advisable thing for the DM to do.
While I’m not suggesting Banning players from using spells, and in the context of this question it’s acceptable
But It’s been stated once you rage you can’t concentrate on a spell, would a t-rex be able to concentrate?
You can’t concentrate while raging because the rules on raging say you can’t. There is no such wording in the description of the polymorph spell, nor do the general rules on concentration including changing shape as something that breaks it. So, you absolutely can maintain concentration while polymorphed. The rules mean what they say, no more, no less.
Why restrict the player from being a T-Rex. Polymorph is already heavily restricted in that you can only polymorph into a beast. As it’s a concentration spell, if the PC then wades in to battle, every attack that lands is going to force a concentration check to maintain the spell…. it’s suddenly not such a good idea and the spellcaster is toe-to-toe with an enemy. Also they have the mental abilities of the creature they turned into but maintain their personality. So you have a clever spellcaster reduced to an intelligence of 2! They are only going to be able to process simple things – attack, run, hide, attack….