You attempt to beguile a humanoid that you can see within range. It must succeed on a Wisdom saving throw or be charmed by you for the duration. If you or creatures that are friendly to you are fighting it, it has advantage on the saving throw.
While the target is charmed, you have a telepathic link with it as long as the two of you are on the same plane of existence. You can use this telepathic link to issue commands to the creature while you are conscious (no action required), which it does its best to obey. You can specify a simple and general course of action, such as "Attack that creature," "Run over there," or "Fetch that object." If the creature completes the order and doesn't receive further direction from you, it defends and preserves itself to the best of its ability.
You can use your action to take total and precise control of the target. Until the end of your next turn, the creature takes only the actions you choose, and doesn't do anything that you don't allow it to do. During this time you can also cause the creature to use a reaction, but this requires you to use your own reaction as well.
Each time the target takes damage, it makes a new Wisdom saving throw against the spell. If the saving throw succeeds, the spell ends.
At Higher Levels. When you cast this spell using a 6th-level spell slot, the duration is concentration, up to 10 minutes. When you use a 7th-level spell slot, the duration is concentration, up to 1 hour. When you use a spell slot of 8th level or higher, the duration is concentration, up to 8 hours.
bloodbending
Im nuking my dominated barbarian with magic missiles so he can throw like 3+(more if upcast) wis saves since you throw the save each time you getting damaged
In my interpretation of RAW, he only gets one save still.
Magic Missile bolts all hit at the same time. They are treated as one instance of damage if multiple hit the same person.
The specific rule this is taken from is (PHB p.196):
If a spell or other effect deals damage to more than one target at the same time, roll the damage once for all of them.
And the Magic Missile spell (PHB p.257) states that the missiles strike more than one target at the same time:
The darts all strike simultaneously
Ergo, Barb only gets 1 save regardless of how many bolts he gets hit with so long as they are all from the same cast.
The Charmed condition does not say the creature considers itself friendly to you, nor does this spell. It states the Charmed creature can't attack the charmer or target the charmer with harmful abilities or magical effects and the charmer has advantage on any ability check to interact socially with the creature. Ergo, it depends on interpretation.
I would say the first save gets advantage and subsequent ones only do if the caster/caster's friends keep attacking it, as the physical act of fighting would have stopped between you in that case. However, it is perfectly reasonable to say that if you are fighting the creature and cast this spell, it still considers itself to be fighting you after being charmed, so it gets advantage on the save. The spell does not specify which it is referring to.
Talk to your DM. I'm sure you can come to a satisfying conclusion.
Here's a ruling on that exact question from the lead rules maker for DnD, Jeremy Crawford. I think you will find this interesting.
https://twitter.com/jeremyecrawford/status/716012166101401600?lang=en
No, because it specifically states, "while the target is charmed..."
If a target is immune to being charmed, then the effects cannot take hold. You would first need to suppress their charm immunity. While there is not a predefined mechanic that suppresses a character's charm immunity (Paladin: Oath of Devotion. Aura of Devotion at level 7), you could use a specialized curse such as from an item or a side-effect of being in the Shadowfell too long. These would be customized curses still.