If the target of Planar Binding fails its Charisma saving throw, it “must follow your instructions to the best of its ability”.
How does the target experience the effects of the spell? What is the subjective psychological and physical impact on the target?
Having some understanding of how the target of the spell experiences “must follow your instructions” can help answer many questions related to this spell. Below, I pose various sub-questions meant to clarify (and add context to) the over-arching question of how the target experiences the effects. Note that there is not a great deal of RAW related to this (that I am aware of), so much of this will be answered with “it is up to DM discretion”. What I’m looking for is guidance around what is sensible in that context (preferably that aligns with game balance, related game mechanics, etc.)
The relevant portion of the spell description:
… first paragraph snipped …
A bound creature must follow your instructions to the best of its ability. You
might command the creature to accompany you on an adventure, to guard a
location, or to deliver a message. The creature obeys the letter of your
instructions, but if the creature is hostile to you, it strives to twist your
words to achieve its own objectives. If the creature carries out your
instructions completely before the spell ends, it travels to you to report this
fact if you are on the same plane of existence. If you are on a different plane
of existence, it returns to the place where you bound it and remains there until
the spell ends.
… third paragraph snipped …
Does the target feel an irresistible compulsion? The description specifically states that creatures hostile to the caster strive to twist the caster words to achieve its own objectives, so the magic of the spell does not magically make the target willing. Does that mean that if a command is antithetical to the nature of the target, they experience continual psychological distress in abiding by the commands of the caster? For example, if an evil Dao is subject to this spell and is commanded (among various other things) to “be kind to everyone you meet”, is this experienced by the Dao as torture? Or does the magic of the spell make it feel natural to do what is commanded of them?
Suppose the caster has a long list of instructions for the target (see “How can an entity bound by Planar Binding be prevented from betraying the caster?” for an example). The spell states “… must follow your instructions to the best of its ability“, which to me implies that it is possible for mistakes to be made. Depending on the intelligence of the target, keeping such a list in mind at all times and being able to see the interactions between competing commands will sometimes be beyond their intellectual abilities in the moment (no matter how intelligent) and they may therefore unintentionally violate some command at some point. What happens to them if this occurs? Are they wracked with guilt? Do they suffer psychic damage? Or are there zero consequences in this situation?
A somewhat related spell is Geas, which specifically states “While the creature is charmed by you, it takes 5d10 psychic damage each time it acts in a manner directly counter to your instructions”. Since Planar Binding does not have any such verbiage, can we assume it is simply impossible for the entity to intentionally violate instructions? If so, how is this experienced by the target? If it is not magically impossible for them to intentionally act counter to instructions, what does keep them from doing so? If their personalities remain intact (as suggested by their attempts to twist words), commands dictated by the caster will inevitably chafe (especially those antithetical to their ethos). So what keeps them from rebelling if it isn’t physical damage, etc.?
Each of Command (1st level enchantment), Suggestion (2nd level enchantment, Compulsion (4th level enchantment), Geas (5th level enchantment), Planar Ally (6th level conjuration) and Mass Suggestion (6th level enchantment) spells specifically disallow “obviously harmful” and/or “suicidal” commands, but Planar Binding (abjuration) does not (note that Planar Binding is the only abjuration spell on the list). Does this mean the target is forced to perform even a suicidal command, or do we read in this exclusion as unintented missing text?
Is the target aware of the binding? There is no explicit mention in the spell description of the target being aware, but the effects of the spell seem like they would be pretty obvious to the target (unless the magic is masking these effects). It all comes back to the question “how does the target experience the effects of this spell?”.
Of the 50+ abjuration spells, a few include effects that influence the behavior of creatures, including ProtectionFromEvilAndGood (disadv on attack rolls), Sanctuary (must make Wisdom save to make attack), and Magic Circle (certain creatures cannot willingly enter AofE, disadv on attacks). Can answering similar questions about how creatures experience the effects described in those spells help shed light on what happens in Planar Binding.
All of these questions are made more pointed when the spell is cast at a higher level. If the entity is bound for 30 days (7th level), 1/2 year (8th level) or 1 year + 1 day (9th level), the question of how the target experiences the spell are more relevant, as it influences how they behave, whether they go into a deep depression, how much planning they can perform to escape the spell (especially when commanded not to engage in such planning), etc.
Here are some initial thoughts as to answers (sadly, they generate more questions). Where do these answers run counter to RAW and/or RAI?
I’m highlighting the fact that Planar Binding is abjuration rather than enchantment, and assuming that this implies some external forcing function enforces the magic rather than the magic affecting the mind of the target (as would happen for an enchantment). But I do not know what this “external forcing function” is (having Mystra have to consciously monitor and enforce every occurrence of every such command seems untentable), and such an external forcing function would seem to suggest that it wouldn’t be possible for the entity to unintentionally violate a command either (but the wording of the spell suggests they can, because of the “to the best of its ability” phrasing). So I’m left with no satisfactory answer to exactly what the target experiences. I do think that commands antithetical to the creature would be experienced as torture (which is disconcertingly horrifying to contemplate, if a Ki-Rin is bound and forced to torture innocence, for example).
The spell does not mention anything about damage, so in situations where the target unintentionally violates a command, I am assuming zero consequences. It can be an opportunity for the caster to ask for an explanation of how the commands were interpreted by the target, and to clarify commands for the future.
The simpliest ruling would be that it is impossible for a creature to intentionally violate the commands (leaving the mechanism unspecified), but that leaves open the question of how the creature experiences this. If they normally lie all the time, but are commanded to tell the truth, do they start to lie only to find the truth coming out of their mouths instead? Or does the thought of lying simply not cross their mind because of the magic of the spell? Does telling the truth feel natural or unnatural? Is the target aware they are doing something contrary to their normal behavior?
Since spells exist that explicitly disallow suicidal/harmful commands, but Planar Binding does not provide such wording, it would seem that this does indeed mean that the target will perform such acts. I would, however, rule that they are allowed another save to break the spell anytime this happens (maybe even at advantage).
It seems more reasonable for the target to be aware of the effects of the spell. On the other hand, if the target is NOT aware of the spell, it means that it feels completely natural to them to perform the actions dictated by the instructions provided by the caster. This resolves many of the other questions (they do not feel mental anguish over following instructions counter to their normal behavior, etc.). So, although the more reasonable answer is awareness, there is a part of me that wants a lack of awareness, because this feels like such a horrifying kind of torture to inflict on something.
If a creature attacks someone who has Sanctuary cast on them, how does the creature experience the magical effect? Game mechanically, they need to make a saving throw, but what is the in-game analog of that save? Are they conscious of some impediement, or does it just feel completely natural for them to attack someone else, without being aware that their behavior was affected by magic? I don’t know the answer to that … I feel another SE question in the making…
I can’t imagine how horrifying it would be to be bound by a caster with an opposite alignment forcing me to do things every day that are antithetical to my ethos. Suicide would be a natural response … except that the caster could command me not to attempt suicide. It is the reason I’m tempted to rule in #5 that the target feels completely natural performing the actions commanded of it.