How Players Can Use Mind Control In Your Game - Without Everyone Losing Their Minds
Spells that control minds such as command, charm, suggestion can really change your game. That's good, right? That's what 'magic' was meant for after all. Say someone uses 'Command' - requiring some NPC or PC to 'masturbate'. Say the slime-covered orc shaman 'Suggests' something rude like "You touch me until i feels gooood", what then? Most mental control spells guard against certain death or even bodily damage - but what about public humiliation or the crossing of unthinkable boundaries? That seems to be fair game in mind control... or is it?
As ridiculous as it sounds, this is a very real problem for everyone at your table. Even as a DM: you have an incubus or succubus: their day-job is to seduce targets, isn't it? That may be just fine for the characters - but D&D is about the experience of the players. The moment a role-playing game offers no choices, there is no game.
So... What Does 'Charmed' Really Mean?
To be charmed is a 'condition' and in 5e it means these two things:
Say you are a wizard in a band of elves and you cast Charm on an orc. This orc may be willing or even thankful to kill their elder brother ('get the inheritance!') - yet strongly refuse to smile at the caster ('bad luck to smile to elves!!'). Also, 'friendly' safety / protection offered by spells will extend to the caster (one person). This charmed orc will still try to slaughter all your friends ('all fae BAD!!').
On this point, almost all the spells that control minds have a means to break them right in the Rules As Written (RAW).
Take suggestion: the example given is a request for a knight to give away his faithful steed to the next person they meet. First off, one must remember that a horse in these conditions is more than just transport to such a person. This is the very symbol of being a knight (and not just a mercenary or thug), a better friend than a dog, and a means of survival in wartime. Even if the knight did 'give' their horse away, they might not be charitable enough to follow through.
You will find people describing the use of suggestion to be similar to being heavily intoxicated. "Remember when we all got really drunk and did that thing?" - this is a great rule of thumb as to how successful this spell might be. Imagine that character-being's very craziest ideas in their cheapest and poorest wisdom. Some might gladly throw a tomato at the king and hope they can get away with it. Others might sooner die before so much as scratching their beloved daughter. Your DM will have to adjuctate on the spot - and hopefully be generous as possible. It is magic after all.