On Shapechanging

If one goes looking for what are commonly considered to be the "problem" spells in 5th edition Dungeons & Dragons, there are some usual suspects which always come up - guidance, find familiar (and summoning in general), healing word, augury (and other divinations), healing spirit, counterspell, tiny hut, simulacrum (and all illusions), wish, and so, so many more. Hyper-online D&D players love to complain about magic in D&D.

I see problems with these spells and others, and have had my share of trouble with magic in D&D, but none of them has ever bothered me quite so much as polymorph, its related spells, and shapechanging magic in general, like the druid's Wild Shape ability.

On Challenge Rating

Polymorph (Player's Handbook, page 266) allows the caster to transform a creature for up to an hour into any beast whose challenge rating is equal to or less than the target. This changes the target's game statistics (including mental ability scores, but not alignment and personality) to that of the beast. 

True polymorph (page 283) uses the same CR = level approach as polymorph, but the new creature doesn't need to be a beast, and the change lasts until dispelled if the caster concentrates on the spell for the full hour. 

Shapechange (page 274) again uses the CR = level approach, but it only affects the caster, the new form needn't be a beast, the caster retains their mental ability scores and skill and saving throw proficiencies, and for the duration the caster can use an action to change shape again.

My problem with this is that the Monster Manual states "An appropriately equipped and well-rested party of four adventurers should be able to defeat a monster that has a challenge rating equal to its level without suffering any deaths" (page 9). In other words, a CR 7 creature is meant to be a challenge for a party of four appropriately equipped and well-rested 7th-level characters.

So...if a CR 7 creature is roughly equivalent to four 7th-level characters, why can a 7th-level character transform into a CR 7 creature, which in and of itself should be a fitting challenge for the entire party? Why does the Monster Manual tell the DM, when building encounters, to equate a CR 7 creature to an entire 7th-level party, but for the sake of this spell and those like it, equate a CR 7 creature with a single 7th-level character?

Mass polymorph (Xanathar's Guide to Everything, page 160) is a bit different - it affects up to 10 creatures, and just like polymorph, the new forms can be beasts only. However, the new form's CR must be equal to or less than half the target's level. I imagine that this caveat is there because it affects more than one creature, but I'm going to interpret it as recognition that an Xth-level character is not equivalent to a CR X monster.

Wild Shape (PHB, page 64) recognizes this too. A 2nd- or 3rd-level druid can Wild Shape into a CR 1/4 beast (i.e., not a CR 2 or 3 beast). A 4th-, 5th-, 6th-, or 7th-level druid can Wild Shape into a CR 1/2 beast. At 8th-level and beyond, they can Wild Shape into a CR 1 beast. The Circle of the Moon druid (page 69) can do a bit better, but even at the height of their powers, they can Wild Shape into a CR 6 beast (at 18th-level) or a CR 10 elemental (at 10th-level, expending two uses of Wild Shape in doing so).

Why is it that a 7th-level bard, sorcerer, or wizard gets access to a spell which immediately allows them to change into a more powerful creature than is allowed by the shapechanging class ability of the shapechangey-est subclass of the game's shapechanging class? (Yes, druids do get access to polymorph too, but that's not the point I'm making.)

Similar to how mass polymorph affects multiple creatures, one could argue that the limitation on Wild Shape is there because the druid can use that ability relatively often (twice per short rest), whereas another spellcaster's spell slots (used to cast polymorph) only return on a long rest. Yet, considering a spellcaster can get up to three 4th-level spell slots per day with which to polymorph - plus more, if they choose to use higher-level slots to do so - this doesn't seem right either.

As an aside, this makes me wish that the Monster Manual or Dungeon Master's Guide included a table which roughly matched characters of a given level to monsters of a given CR, i.e., a CR 1 monster is roughly equivalent to a 3rd-level character - something like that. It would make so many things easier - not just this specific issue, but also encounter balancing (when I feel the need to do that), and designing player characters as monsters and vice versa. 

Want to stat up a 20th-level cleric as a PC and convert them to a monster/nonplayer character? Here's what CR they should be. Want to give a red dragon wyrmling sorcerer levels? Well, a CR 4 creature is roughly equivalent to a 6th-level character, so they can have 6 levels of sorcerer (granted, this would effectively change the CR, but let's be honest - those monsters need some beefing up).

Xanathar's Guide to Everything has something similar in Chapter 2: Dungeon Master's Tools, under Encounter Building (page 88), which gives guidelines for how many creatures of a given CR to use in an encounter against a number of characters of a given level, but these tables also make the laughable claim that a 20th-level character is roughly equivalent to a CR 7, 8, 9, or 10 monster, so I don't really trust that math.

On Hit Points

Perhaps the more problematic element of polymorph is this: "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." All of the aforementioned shapechanging spells work this way, save for mass polymorph, which does the same thing but with temporary hit points for whatever reason (precluding the affected creatures from benefiting from additional sources of temp HP or from healing), and shapechange, which specifies that when the target changes their form additional times, they don't assume the hit points of their new form if it has more hit points than their last form.

So the sorcerer twins a polymorph spell to target the 8th-level barbarian and fighter, turning them both into tyrannosaurus rexes (D&D is a silly game, which is a good thing). They stomp into combat against the dragon, take 136 points of damage each, then revert to their humanoid forms and...still have their full 100 hit points or whatever from before they were changed.

I thought this was shapechanging magic - I didn't realize the spell encases the target in a t-rex-shaped shell which wards them against harm until the enemy does enough damage to break them out of it. The way I understand it, the target's body is transformed - the t-rex form is still their body. It's body takes damage, the target's body takes damage.

"Well, the target's armor class is usually worse when they transform into a beast, so if they're easier to hit and still take damage as normal then the spell just sucks!" one might say, to which I would say, "No it doesn't!"

The benefit of polymorph and its ilk is that the target can assume myriad forms to suit any situation. With the use of one spell or class feature the affected creature can climb, burrow, fly, swim, become faster, stronger, better able to concentrate on spells, gain new proficiencies, heightened senses, and - with more powerful magic like shapechange, true polymorph, and Elemental Wild Shape - squeeze through cracks as narrow as an inch wide, gain immunities and resistances, cast spells, unlock a new suite of supernatural actions, speak new languages, wield a flame whip and lightning sword (assuming your new form gets the typical equipment included in its statblock, which - don't get me started), and even with all that, they retain their alignment and personality.

So yeah, the tradeoff should be that the target's body is their body and their hit points are their hit points.

Changing Shapechanging

I like that in D&D a creature can change into a dragon or a beholder or a giant or whatever. I really do. It's an awesome ability, but, I also get tired of the t-rex polymorph meta. Shapechanging magic is immensely powerful without having game-changing combat utility. In my most recent 5e game, the warlock spent levels 17 to 18 as a death knight and level 19 as a balor. 

It was really cool when they first did it, but for three whole levels in the last tier of the game, they weren't even playing a warlock anymore, because it was just so much better to transform into an "equivalent" monster. If they really wanted to, they could have permanently transformed the whole party into balors (again, pretty cool, but it feels wrong somehow - they also would have stomped every encounter for the rest of the campaign, easily).

So, I'm done with polymorph as written. My house rule for shapechanging mechanics is presented below:

When a creature changes shape (such as with the polymorph spell), a player character can change shape into a creature whose CR equals (at most) half the character’s level (rounded down), unless the feature specifies that the character can only change shape into a creature with a lower CR (i.e. the Wild Shape class feature). When a creature’s new form is reduced to 0 hit points, it reverts to its normal form. Any hit points lost during the transformation are subtracted from the character’s current hit points.

For example, a 20th level wizard with 142 hit points uses polymorph to transform into a CR 8 tyrannosaurus rex with 136 hit points. The wizard’s tyrannosaurus rex form is reduced to 0 hit points, and the wizard resumes their normal form. The wizard now has 6 hit points (142 - 136 = 6).

Shapechanging abilities grant you only the physical traits of the new form. You always retain your Intelligence, Wisdom, and Charisma scores when you change shape, along with any saving throw or skill proficiencies associated with those scores. You do not gain access to any abilities, actions, proficiencies, or spells which the new form has if those features use Intelligence, Wisdom, or Charisma.

Side Note: I have a second house rule for Circle of the Moon druids which grants them 4 temporary hit points per druid level when they Wild Shape (based on the Circle of Spores's Symbiotic Entity feature - Tasha's Cauldron of Everything, page 36), so that Wild Shape maintains some combat utility for them in light of this change. I would also rule that the limitation on CR doesn't affect Elemental Wild Shape, since that feature specifies that you can transform into a more powerful creature than would otherwise be allowed, and specific rules trump general rules in 5e.

System Shock

When I first decided to change shapechanging in my games, I first looked back at Advanced Dungeons & Dragons 2nd edition, it being my "older edition" reference point. It was definitely still a mess back then, including a complicated and poorly laid out system for polymorphing creatures and objects, for which the duration changes depending on the difference between the kingdom, class, "relationship", size, shape, and intelligence of the creature or object and what it is being turned into (2e PHB, page 242). For example a lion can be polymorphed into a sphinx permanently - because a sphinx is like a lion - but a turnip can only be polymorphed into a purple worm for a few hours - because a turnip is not at all like a purple worm. That is the extent of the guidance given.

2e also has cool ideas like polymorphing a creature into a rock and grinding the rock into dust to kill them, but if one polymorphed the creature directly into dust they'd have to "scatter the dust far and wide" in order to effectively kill the creature. I have no idea how I would apply this to 5e, but it is inspiring.

2e also includes system shock (2e PHB, page 21), which is a percentage chance - based on a character's Constitution - to survive body-altering effects like polymorph, petrification, and magical aging. On a failed system shock roll, the change is so devastating to the creature that it dies instantly. The check is made when the creature changes shape and when it reverts to it original form (page 205). Notably, it doesn't apply to the polymorph self spell, so I think the check is only required if the change is done to an unwilling creature.

If I were to introduce system shock to 5e, I'd probably do it as such:

Whenever a creature is unwillingly subjected to a magical effect which reshapes or ages its body (petrification and reversing petrification, shapechanging, magical aging, etc.), that creature may be instantly killed by the shock to its body and mind. The creature must make a DC 10 Constitution saving throw or instantly die.

I wouldn't necessarily encourage this, as it only enhances polymorph's ability to be a pseudo-death spell, which it already is in 5e, if Rules-As-Written white room theory-crafters are to be given credence. Basically, the caster transforms the enemy into a vulnerable creature like a sheep and then surrounds the target with their allies, readying to attack all at once so that the entire party's focused damage is applied simultaneously, before the creature reverts to its original form. 

This is incredibly cheesy and I would never allow it (the first hit to drop the target to 0 hit points would cause it to revert to its original form, in my opinion - roll initiative to see who strikes first), but I thought I should address it in case Redditors decide to nickel and dime me on this point.

Interestingly, polymorph self in 2nd edition (PHB, page 206) only allows the affected creature to benefit from the new form's movement and breathing abilities. However, they can change shape as often as they please while the spell lasts, similar to 5e's shapechange. This was my inspiration for making it so that shapechanging in 5e only grants you the creature's physical capabilities, not mental ones.

Retaining Personality

I always love to make it a point whenever polymorph comes up in my 5e games that the affected creature retains its alignment and personality. "Don't worry, friends - you can tell that the tyrannosaurus rex is me, your loyal ally, because it has my personality and mannerisms."

Don't worry, this is actually the party's barbarian!

2e has another interesting mechanic by which a polymorphed creature might assume the personality of (and believe itself to truly be) the creature it's polymorphed into (PHB, page 205). A percentage chance is calculated based on the difference in Intelligence and hit dice between forms. The polymorphed creature must roll against this percentage each day it's polymorphed, and on a failure, it effectively becomes the new creature and comes under the control of the DM until recovered by a wish spell or similar magic. This total transformation includes the acquisition of all the new creature's magical and special abilities (like a dragon's innate spellcasting and breath weapon). Furthermore, those who are reverted to their original form after this transformation has occurred maintain the belief that they are actually the polymorphed creature and attempt to return to that form.

Again, this doesn't apply to the polymorph self spell, so it might apply to unwilling creatures only. However, polymorph any object (2e's version of true polymorph - PHB, page 242) does state "The system shock roll must be applied to living creatures, as must the restrictions noted regarding the polymorph other and stone to flesh spells." Which restrictions are we referring to?

Stone to flesh (2e PHB, page 230) has some language about the cubic volume of flesh and stone that can be converted (with a delightful mental image of a wizard creating a tunnel of flesh through a solid stone wall), as well as some language about broken or weathered petrified individuals retaining their damage and deformities when unpetrified, so either or both of these might be the aforementioned "restrictions".

The "restrictions noted regarding the polymorph other...spell" might then be the note about retaining personality when polymorphed. This is how I choose to read it, as although the target of the polymorph any object spell could be willing or unwilling (and previous examples suggest that only unwilling targets are at risk of losing their personality), it makes perfect sense that a creature which spends days, months, or years polymorphed into a demon might be at risk of believing themselves to actually be a demon.

A scientist (AKA modern day wizard) who turns themselves into a fly may be at risk of believing themselves to truly be the Brundlefly.

This becomes a potential solution to the true polymorph problem, wherein a 17th-level character expends one 9th-level spell slot one time and proceeds to spend the rest of their adventuring days in the form of a death knight or balor with no risk of consequence. If I were to use such a mechanic in 5e, I'd do it like so: 

Whenever a creature is subjected to a magical effect which reshapes its body into that of another creature, there is a chance that the creature assumes the alignment, personality, and mental ability scores of its new form. 

At dawn each day after the creature is first transformed, the creature must make a Charisma saving throw. The DC equals 10 plus the difference in Charisma between forms (if the new form's Charisma score is higher) or minus the difference in Charisma between forms (if the new form's Charisma score is lower), plus the difference in levels or CR (if the new form's level or CR is higher) or minus the difference in levels or CR (if the new form's level or CR is lower). 

On a failed saving throw, the creature assumes the alignment, personality, Intelligence, Wisdom, and Charisma scores of the new form, gains all associated abilities and proficiencies, and comes under the control of the DM. The transformation can be reverted as normal, but changes to alignment, personality, mental ability scores, associated abilities and proficiencies, and control of the creature by the DM can be reverted only by way of a greater restoration or wish spell, or similar magic. Until that time, the creature believes itself to be its new true form and attempts to return to that form.

I'm using Charisma instead of Intelligence here, because Charisma in 5e is a creature's "force of personality" (PHB, page 173), and this is a contest of personality/sense of self. I'm tempted to leave it as Intelligence, because Intelligence needs all the help it can get in 5e, but Charisma feels like the "right" ability score to use. 

I'm using CR instead of hit dice because CR is the measure of a monster's power in 5e, whereas the same can be said of hit dice in 2e.

Again, I like that shapechanging magic can accomplish such goofy and cool effects. PCs should be able to transform into powerful monsters at a certain point in the game, but the conversion rates are whacky, transforming into a t-rex every combat is boring after the first time, and one shouldn't be able to live out their days as a dragon without risk of consequence. 

Shapechanging magic is extremely versatile without being the dominant meta-strategy in combat during the later tiers of gameplay. I like its combat potential reined in, its mechanics more sensible, and its drawbacks more nuanced - or rather, in 5e, I'd like it to have any drawbacks at all!