Swallow Whole and polymorph spells.

[Yqatuba]

If someone with polymorph type spells get swallowed whole but then tries to grow into something too big to fit what happens? Does the caster burst out of the monsters chest like on Alien?

[Pizza Lord]

Since this is General Discussion, and not Rules, I would say a fair call would be to use the size changing rules where if you can't expand fully that you expand to the maximum available size and stop (unless you burst the enclosure).

In this case, I would say if a creature could contain 1 large creature and you polymorphed or otherwise increased in size to large, you would still be inside. If you increased (or tried to increase) to huge, you would get a free check (based on Strength) to escape and climb out (you wouldn't burst out of a creature). You would then be grappled and held in the creature's mouth (assuming it was able to hold a creature of your new size). This might also happen if there are too many creatures swallowed, such as if a creature could hold two medium creatures or one large creature and one of two swallowed medium creatures tried to become large.

If you failed the burst/grapple check to escape, you would stop growing at the maximum size. I would say this could lead to some strange-sized creatures, such as a medium warhorse or ogre or something else if you weren't able to grow fully (or you could just have the spell fail, but I don't think that's needed).

I would say this is probably a fair ruling in cases where a creature is shrunken or reduced as well and the effect ends. I would restrict their return to normal size until they have room to grow (rather than having them compressed into a pressurize red spray, though there have been several gruesome traps that utilize this mechanic).

[Claxon]

Generally speaking the amount of HP damage required to escape is pretty low, but I agree that the mechanics don't cover this...as a GM I would also that you make a check to escape. If you fail you don't grow to full size, and if you succeed you escape, no damage to the swallowing creature.

Why? Because honestly swallow whole is a terrible ability in the first place, and we don't need size changing shenanigans to instantly kill the creature.

[KujakuDM]

Vore Joke.

Moving on.

It's magic, I personally would treat it as such, the rules dont change and if they escape they escape with no change to the effects of the ability.

[pjrogers]

We had this happen recently in a game and fell back on the rules found under Enlarge Person

"If insufficient room is available for the desired growth, the creature attains the maximum possible size and may make a Strength check (using its increased Strength) to burst any enclosures in the process. If it fails, it is constrained without harm by the materials enclosing it–the spell cannot be used to crush a creature by increasing its size."

[Scrapper]

Order of the Stick #638 http://www.giantitp.com/comics/oots0638.html
Sorry, not sure how to make links live...

[blahpers]

I mean, they never even resolved the feather token (tree) version of this trick. As far as I can tell, spontaneous treesplosion is a thing.

[Val'bryn2]

I would probably rule that the monster coughed you up as you were enlarging.

[cyandb]

The reverse of this happened in a game I was in. The fighter got swallowed, then I baleful polymorphed the offending creature. DM ruled the fighter did a Kool-Aid man effect. Fighter took some crushing damage, but it was totally worth it.

[MidsouthGuy]

I've had a similar thought about creatures that can shift into forms that change their size. Like, what happens if a dragon eats an entire cow and then shifts into human form? Does the food it ate shift forms with it? Or does it have to wait until its meal is digested and passed before changing forms?

But to answer your question, I am pretty sure they would get to make a strength check to escape (either out the mouth or by carving a new exit) and if they fail then the polymorphed character just increases in size as much as it can in the available space. Which could end up very uncomfortable for whatever ate them, so it might puke them up anyway.

[Kayerloth]

I'm with Val'bryn2 on this one for the most part. "Expanding" will generally force you to fill whatever space is available and then continue forcing continued expansion into the path of least resistance, i.e. back up the way you came possible to get chewed on a bit as you pass back out the mouth and land 'plop' in front of the creature in question. Pretty much what generally happens if, for example, the family dog eats a loaf of frozen uncooked bread dough. It thaws, yeast does its thing and before long he's wandering around your carpet puking up all that nice bread dough, mucus, grass and whatever else he decided to eat for breakfast.