The caster gives the target a verbal command (which they should be careful how they word).
The magic of this spell enables the target to understand the caster, even if they do not share a language. Deaf targets are normally unaffected.

The target gets a social save against this curse.

Pass:
If the target passes its save, the target is completely unaffected by this spell.

Fail:
If the target fails its save, it is compelled to follow the caster’s command to the best of its ability. Following the command becomes the target’s top priority, and they will stop whatever they are doing (unless it is relevant) to pursue completing it.

Whenever a creature is about to be compelled to take an action which will obviously result in harm to itself or things it cares about, it gets another social save to end this spell before it must take that action.
Obviously suicidal commands automatically break this spell.
The limits on what a target can be commanded to do are determined by the Headmaster, but as a rule of thumb, command is a powerful spell and can be used to do things up to and including making enemies try to kill their allies.

While under this spell, the target is an observer of their actions. With particularly disagreeable commands, a war rages inside of them, and their suppressed will and consciousness struggle to regain control as they are forced to watch and silently and futilely scream out in protest while their body complies. A commanded creature often seeks to defeat or escape the spell, but its hold on them is absolute.
Since telling anyone else about being under a command spell carries some risk of them taking countermeasures or the spell being dispelled, which may interfere with completing the task, the target of a command spell is forbidden from talking about or even implying they are under the spell. If they are asked about it, they may find themselves lying.

Instructions Unclear:
Command does not give the caster complete control over the target, and the spell must respect the wording of the command. As such, the target’s will may steer them toward an interpretation of the command that they find more agreeable than the one intended by the caster, including maliciously compliant interpretations.

This spell leaves behind a curse on the target which may be dispelled or lifted, freeing them from the compulsion to carry out the command.
It is hard to detect that the target is cursed by examining them using Spellcraft,
it is harder to detect the target is cursed by the command spell,
and it is even harder to see the exact words of the command which are embedded in the magic of the curse.

You cannot end this curse once it has been cast.
You may cast Command again to countermand your original Command, dispelling it if the target fails their save against the spell.
If a target receives two conflicting commands, a contest of Spellcraft between the casters of those commands determines which command takes precedence.

This spell can be used across a social network, even if it would not normally be able to target the creature (ex: the creature is too far away), or the target is deaf.

Suggested Backfire: The creature gets to command you to do something.

When you cast Command on a creature that you are touching, you do not have to speak the command aloud, and you may command the target telepathically instead.
This allows your Command to affect a deaf target.

When you cast Command, instead of issuing a command, you may store the Command in a magical seal on the target for later use by devoting the spellburn used to cast it if the target fails its save.
(Your maximum spellburn die size is reduced by one stage until the delayed command is used or dispelled.)

This delays the spell’s effect and forms a magical link between you and the target. The target gains a visible brand somewhere on their body which lasts until you use the stored Command or the curse is broken. The time the Command spends as a latent brand does not count against its duration. You may telepathically communicate with a creature that bears your brand.

As an action, you may choose to activate the stored Command to cast Command on the branded target for free, and they automatically fail the initial save against it.

Your Command spell can only be identified by a critical success on a test of Spellcraft.

When a target fails its save against your Command spell, you may place a permanent memory modifying enchantment on them that makes them forget that you commanded them to do something.

They will still feel a compulsion to carry out the command, but will not consciously recall the spell being cast on them, that they have been commanded, or what the command was.
The target may rationalize why they did what they did if your command was not strongly opposed to their nature or beliefs.
If the command is strongly opposed to their will, when its compulsion grips them, they will know something is up, but it may be hard to figure out who told them to do what.

A creature can be affected by multiple memory modifying enchantments at the same time.
If the memory modifying enchantment is dispelled, the creature regains its memory of events.

When your Command spell ends because a creature carried out the command, you may choose to leave a permanent memory modifying enchantment on the target, which deletes their memories of what they did while under the Command spell.
They will have no recollection of what they did while under this spell, and the last thing they will recall is being given the command.

A creature can be affected by multiple memory modifying enchantments at the same time.
If the memory modifying enchantment is dispelled, the creature regains its memory of events.