Friends is a strange spell because it tells you how to roleplay the targets reaction without exception. However, it also give a reasoning for the reaction.

When the spell ends, the creature realizes that you used magic to influence its mood and becomes hostile towards you.

However, what happens if you warn the target beforehand that you are using the spell? For example, if you are a performer and you want a person to "experience the music in a heightened state." You explain what the spell does and they agree to have it done to them.

1. Is the hostility some sort of magical compulsion or just the assumed reaction to the deception?


2. Does it matter at all that the reasoning behind the reaction isn't true anymore?


3. If it is magical, how long does it last afterwards?

No, except by DM discretion

The spell states:

When the spell ends, the creature realizes that you used magic to influence its mood and becomes hostile towards you. [...] Another creature might seek retribution in other ways (at the DM ’s discretion), depending on the nature of your interaction with it.

The creature simply becomes hostile towards you after the spell ends because the spell causes them to become so. The nature of the hostility (and resulting behavior) is up to the DM, including attacking you, refusing service afterward, giving false information, or other. In the case of full disclosure beforehand, the creature hostility might manifest in subtler ways, maybe fueled by doubt that you cast the right spell or other reason.

The change of mood is caused by the spell, thus it is magical, but since the spell already ends, the hostility is not fueled by the spell, thus it is not dispellable. The duration is also not specified, so it defaults to indefinite. The hostility, however, is reversible using mundane means, including persuading, intimidating, or whatever course of actions the DM deems appropriate.

The hostility is part of the spell description.

And this is very balanced. This is a cantrip that can be cast once every round as many times as you want. If it were not balanced with a negative response by the target it would be very easy to overuse it. The hostility aspect of the spell does two things:

• It ensures that the target knows who cast the spell when the spell ends.


• It balances the cantrip with a negative consequence.

Both of these points are clearly illustrated in the spell description as shown by the highlighted text (PHB 244, emphasis mine):

When the spell ends, the creature realizes that you used magic to influence its mood
and becomes hostile toward you.

The roleplay is not specified

But it is indicated in a general way. The target becomes hostile. What does this mean? In standard usage for the spell it probably would mean that the target is angry that their feelings were manipulated, or something along those lines, and the target acts in angry way towards the spell caster. However in this usage it could mean something else.

For example, even when a person knows that their mood has been influenced they are often in a state of emotional and even physical discomfort when an "enhanced mood" wears off. Think of caffeine or nicotine withdrawal. You know you had caffeine, you know it made you feel more awake and "perky", you know you would not have made it through the work day without it. It's 5pm, it's affects are gone, and you're annoyed.

How are you annoyed? Do you have a headache? Are you fidgety? Are you exhausted? Do you yawn every ten seconds? What are you annoyed at? The caffeine? The coffee? The work day? Yourself? Traffic? Everything? How do you respond to this annoyance? Do you drink more coffee? Drink some calming tea? Speed in your car? Yell at people? Listen to music?

GM decides the roleplay

There are many ways to feel and act hostile towards a person. In the situation you describe, where the target is knowingly affected by the spell to enhance a performance there are many possibilities:

• The target could be irritable and want more of the spell to continue to feel good.


• The target could want to experience the performance again (right now!).


• The target could feel that the enhancement wasn't all it was cracked out to be and wants their money back.


• The target could be on a downer after such an amazing "enhanced" performance and be generally angry at everything around them.


• The target could be acutely aware that this was the best performance they will ever see and no performance will ever match it because of the enhancement you provided - you essentially just ruined every future performance they will ever see, and they know it. This makes them very angry.


• The target could demand that you accompany them next Saturday night to a different performance that you're not even a part of.

These are just some possibilities.

How the target is roleplayed is entirely up to the GM and there is a vast spectrum of possibilities.

It is possible according to the spell description, but is up to DM discretion

The spell text for friends includes the following:

When the spell ends, the creature realizes that you used magic to influence its mood and becomes hostile ...

[The target] might seek retribution in other ways (at the DM’s discretion), depending on the nature of your interaction with it.

This suggests to me that the outcome it is indeed dependent on the target's prior consent, and the specific actions you take while they are under the spell's effects. In particular, there is no clause stating that the target forgets its consent to influence.