Polymorph + forcecage, deathtrap, or dud?

[dehro]

Say you manage to cast polymorph on a large/enormous creature and turn it into something medium or small...
after a little while you cast forcecage on it.

is the result a meatpaste?
does the polymorph hold until forcecage fails?
does the return to its original size shunt the creature out of the cage?
does the cage fail prematurely?

[Darc_Vader]

I don’t think there’s any specific rule about that, but I’d probably say Polymorph would hold until there’s room. Tellingly, Enlarge accounts for lack of space on casting, but Reduce doesn’t on returning to normal, so it looks like it’s generally going to be a dm’s opinion.

[dehro]

and your call would be to have the polymorph stick around...
makes sense, otherwise this could easily become a way to doubletap/oneshoot even the worst opponents.

[MoiMagnus]

I'd give the precedence to this sentence of the spell: "Creatures only partially within the area, or those too large to fit inside the area, are pushed away from the center of the area until they are completely outside the area."

Even though you could read this sentence as implicitly only applying at the moment of casting the spell, you could also interpret it as a general rule on how to deal with an imprisoned creature being bigger than the cage.
Additionally, this case is clearly a "magical mean of leaving the cage", so the sentence "A creature inside the cage can't leave it by nonmagical means" doesn't prevent you from leaving the cage that way.

I'm not saying that this interpretation is perfect, but it matches the text and it doesn't give rise to absurdly powerful abuses, so I don't really see why I wouldn't take it.

[Chronos]

There's no rules for this, but based on rules for similar situations, I think it'd be most in the spirit of the rules for the creature to shunt outside of the cage when the polymorph ends.

[Yakk]

Obviously idnoclip

[dehro]

Obviously idnoclip

[Gtdead]

Good thing this scenario is so unlikely to happen that it doesn't really matter. I'd rule that the creature pops out of the forcecage once it reverts to it's original size.

[Segev]

There are more interesting interactions. Polymorph and similar spells replace stat blocks entirely, including hp. Normally, this combines with the "when you hit 0, you revert and the damage rolls over" rule to make these alternate forms into hp buffers. However, anything that expressly interacts with the number of hp the target has or which does something upon knocking the target to zero hp is pretty potent.

Wraiths insta-kill things that fail a Constitution save after being knocked to 0 hp by the wraiths' attacks. A low-con, no-hp form therefore is a death sentence if a wraith is nearby.

Power word spells only care about the targets' total hp. Low-hp forms thus render them vulnerable. Same with sleep; nothing says that the creature wakes up if its hp increases, either. Obviously, now you're using a debuff of higher level AND sleep, so it's hardly broken, but consider these as options when the shape changing was legitimately meant to buff the enemy. IF they're getting low in their temporary form's hp, you can use these on them to ensure they don't get a "refresh" of their hp by reverting.

[Snownine]

I think they are reffereing to the idclip and idspispopd cheat codes from the old Doom games that allowed the player to walk through walls and obstacles.


Edit: correcting assumption.

[Porcupinata]

I've not encountered that exact situation, but I have had similar situations crop up in my games. One classic being when a druid was wildshaped into a spider to eavesdrop on a meeting, and someone who knew of the party's plan to have the druid do that (and therefore knew that the spider was secretly the druid) sneaked up and caught them and put them in a glass jar - raising the question of what happens when the wildshape runs out.

As others have mentioned, there's no RAW solution.

My group agreed on the following generic house-rule for this type of situations, so that there would be consistency:

If a magical effect would grow or transform a creature or object into a form that won't fit into its current location, the magical effect fails. If a magical effect has already transformed a creature or object into a form that will fit into its current location and its duration ends but the cessation of that effect would cause the creature or object to revert to a form that won't fit, the effect remains until the creature or object is in a space large enough for it to revert and then immediately ends.

There might still be a couple of edge cases, but most of the time players (and NPC spell casters) know what to expect when they use transformative magic so it saves on arguments and disagreements at the table.

[Greywander]

My group agreed on the following generic house-rule for this type of situations, so that there would be consistency:

If a magical effect would grow or transform a creature or object into a form that won't fit into its current location, the magical effect fails. If a magical effect has already transformed a creature or object into a form that will fit into its current location and its duration ends but the cessation of that effect would cause the creature or object to revert to a form that won't fit, the effect remains until the creature or object is in a space large enough for it to revert and then immediately ends.

I feel like this is potentially open to exploitation by allowing you to force an effect to persist when it should end. For example, if you wanted an ally or enemy to maintain a particular form indefinitely. As an alternative, you could have the creature revert to their original form, but not necessarily their original size. Size will revert as soon as there is enough room, and they'll experience a partial reversion in size up to however much space there is. If they gain any benefits or penalties as a result of the size change, those no longer affect the target, even if their size hasn't reverted yet. For all intents and purposes, the effect has ended except for the size change, which will revert as soon as it can.

Even this could be exploited, though. For example, you could Reduce a creature and then keep them hidden indefinitely, and once you retrieve the creature they would immediate return to their normal size. The only ruling that I think avoids exploitation is to shunt the creature into the nearest open space that can accommodate them. And actually, what if you Reduce yourself, crawl through a passage that is normally too small for you, and ends at a wall with a room on the other side? Technically, the nearest open space is the room, so you'd be shunted through the wall, rather than back down the passage.

I guess everything is exploitable, it's just a matter of finding the least disruptive exploitation. Something good to keep in mind is that if they can, they will, so any exploitation of a spell is likely to be used by spellcasters in-universe (i.e. it's a feature, not a bug), unless it's more trouble than it's worth. This is why something like the Wish-Simulacrum chain shouldn't be allowed; because if it was then every high level wizard would use it, and it would break the setting. If the PCs can do it, then the NPCs can do it, too.

[Porcupinata]

I feel like this is potentially open to exploitation by allowing you to force an effect to persist when it should end. For example, if you wanted an ally or enemy to maintain a particular form indefinitely. As an alternative, you could have the creature revert to their original form, but not necessarily their original size. Size will revert as soon as there is enough room, and they'll experience a partial reversion in size up to however much space there is. If they gain any benefits or penalties as a result of the size change, those no longer affect the target, even if their size hasn't reverted yet. For all intents and purposes, the effect has ended except for the size change, which will revert as soon as it can.

Even this could be exploited, though. For example, you could Reduce a creature and then keep them hidden indefinitely, and once you retrieve the creature they would immediate return to their normal size. The only ruling that I think avoids exploitation is to shunt the creature into the nearest open space that can accommodate them. And actually, what if you Reduce yourself, crawl through a passage that is normally too small for you, and ends at a wall with a room on the other side? Technically, the nearest open space is the room, so you'd be shunted through the wall, rather than back down the passage.

I guess everything is exploitable, it's just a matter of finding the least disruptive exploitation. Something good to keep in mind is that if they can, they will, so any exploitation of a spell is likely to be used by spellcasters in-universe (i.e. it's a feature, not a bug), unless it's more trouble than it's worth. This is why something like the Wish-Simulacrum chain shouldn't be allowed; because if it was then every high level wizard would use it, and it would break the setting. If the PCs can do it, then the NPCs can do it, too.

Yeah, basically if you want to avoid any exploits or edge cases you either need to be arbitrary or you need to have a huge amount of legalese with exceptions and conditions - neither of which are particularly desirable if you're looking for something that's consistent and simple to understand/remember.

[Keravath]

I've not encountered that exact situation, but I have had similar situations crop up in my games. One classic being when a druid was wildshaped into a spider to eavesdrop on a meeting, and someone who knew of the party's plan to have the druid do that (and therefore knew that the spider was secretly the druid) sneaked up and caught them and put them in a glass jar - raising the question of what happens when the wildshape runs out.

As others have mentioned, there's no RAW solution.

My group agreed on the following generic house-rule for this type of situations, so that there would be consistency:

If a magical effect would grow or transform a creature or object into a form that won't fit into its current location, the magical effect fails. If a magical effect has already transformed a creature or object into a form that will fit into its current location and its duration ends but the cessation of that effect would cause the creature or object to revert to a form that won't fit, the effect remains until the creature or object is in a space large enough for it to revert and then immediately ends.

There might still be a couple of edge cases, but most of the time players (and NPC spell casters) know what to expect when they use transformative magic so it saves on arguments and disagreements at the table.

I think that there is still a lot of room for abuse of such a house rule.

The most obvious is to polymorph a really powerful opponent and then drop them into a metal box or glass jar as in your example. The spell never ends this way and you can create a collection of bottled villains that starve and die in their polymorphed form since it is prevented from changing back.

The alternate suggestion that if a creature can't fit into the container when the magical effect ends finds themselves magically outside the container in the nearest location that has sufficient space for them is probably more manageable. There could still be some abuses made but overall it tends to limit what can happen.

[MoiMagnus]

Yeah, basically if you want to avoid any exploits or edge cases you either need to be arbitrary or you need to have a huge amount of legalese with exceptions and conditions - neither of which are particularly desirable if you're looking for something that's consistent and simple to understand/remember.

If you only want to avoid disruptive exploits, there is often one resolution which is better at avoiding them (which some would qualify to be "the boring one"). For example, here, "the creature gets expelled out of the forcecage as if forcecage was just cast on the creature" only creates exploits that might allows to nullify the effects of forcecage more often than intended. And you usually don't get very far with exploits like this one.

[BerzerkerUnit]

If you only want to avoid disruptive exploits, there is often one resolution which is better at avoiding them (which some would qualify to be "the boring one"). For example, here, "the creature gets expelled out of the forcecage as if forcecage was just cast on the creature" only creates exploits that might allows to nullify the effects of forcecage more often than intended. And you usually don't get very far with exploits like this one.

I agree here. Think of it like this: If a player (medium creature) was in a medium crate and cast Enlarge on themselves after getting into a fetal position (maybe to pop out in an ambush), would it fail bc when they stand up they wouldn't fit, even though folded up as they are, they would fit into the crate?

Here's my rule:
If a Spell that does not have explicit damage or hit point reduction rules would incidentally deal damage, it deals 1d8 Necrotic damage per level of the spell. Enemies will usually receive a Dexterity or Constitution saving throw to avoid the damage of cantrips or reduce the damage of leveled spells by 1/2. At the DM's discretion, other damage types can be dealt depending on circumstance.

I default to necrotic bc it seems to be the blood loss/tissue damage type.

Example: I'm a pacifist cleric with no damaging spells, but in an emergency I cast Create Food and Water over the head of a foe. The foe gets a dex save, on a failure takes 3d8 bludgeoning as a bunch of hams and water fall on his head, half damage on a successful save.

If I stuck my hand in his mouth and created the food there, he'd make a Con save or take 3d8 necrotic as the sudden explosion of gallons of water and corn cobs painfully balloon his inside parts before spewing out like a grog fountain.

With the polymorph/forcecage (and any size change shenanigan) I'd rule the target will take Xd8s based on the level of the size changing spell. I would then rule the target is Restrained by the cage (no save) or restrained and still trapped inside the cube but in an uncomfortable cramped position. Other types of containers would be ruled based on type.

(so a troll made a mouse in a glass jar would expand, take 4d8 slashing as he exploded out of the jar while changing back).
If more than one creature were in there they'd also take the damage with a chance to save. So yes, the big creature play-doh fun factory's out the sides of the cage or the top of the adamantine bottle, but the expansion and transformation leaves them more pinched and stuck than flayed alive.

Just saying d8 x level of spell for anything has really streamlined a lot of spells and made me say Yes to players trying to do creative stuff more readily.

[Keravath]

If you only want to avoid disruptive exploits, there is often one resolution which is better at avoiding them (which some would qualify to be "the boring one"). For example, here, "the creature gets expelled out of the forcecage as if forcecage was just cast on the creature" only creates exploits that might allows to nullify the effects of forcecage more often than intended. And you usually don't get very far with exploits like this one.

The obvious one being ...

If a creature inside a forcecage casts enlarge on themselves, so they would no longer fit, are they expelled from the cage?

[Porcupinata]

I think that there is still a lot of room for abuse of such a house rule.

The most obvious is to polymorph a really powerful opponent and then drop them into a metal box or glass jar as in your example. The spell never ends this way and you can create a collection of bottled villains that starve and die in their polymorphed form since it is prevented from changing back.

In theory, yes. However, by the time your enemy has you polymorphed and on your own without friends to prevent that kind of thing they've basically got you at their mercy anyway so it's no big deal. Besides, things like coming across a prisoner trapped inside a bottle in a villain's lab who you can rescue by smashing the bottle is totally genre-appropriate for D&D-style fantasy.

So while it's possible to do that to a powerful opponent, it's not really "abusive" since it's not terribly overpowered compared to the alternatives and it doesn't break the theme of the game/genre in a jarring way.

I'll take smoother play and more consistent expectations at the actual game over some theoretical loophole any day.

[Witty Username]

Say you manage to cast polymorph on a large/enormous creature and turn it into something medium or small...
after a little while you cast forcecage on it.

is the result a meatpaste?
does the polymorph hold until forcecage fails?
does the return to its original size shunt the creature out of the cage?
does the cage fail prematurely?

I would meatpaste, forcecage + moonbeam is already a hard kill so balance isn't a concern and loopholes are too few and far between on 5e anyway.

metal boxes would break under the crushing weight of dragons, dragon takes 1d6 damage. that seems fair.

[MoiMagnus]

The obvious one being ...

If a creature inside a forcecage casts enlarge on themselves, so they would no longer fit, are they expelled from the cage?

Enlarge explicitly calls out this case "If there isn't enough room for the target to double its size, the creature or object attains the maximum possible size in the space available.", so it doesn't work.

But assuming you find a way to enlarge yourself by an effect that doesn't have this restriction, then I'd say that you getting out of the cage is not a really disruptive exploit, and I might rule in favour of it. Teleportation allows you to escape (up to a Cha save), so it's not like the cage is inescapable once you start using magic.