It is possible for a night elf mage to mind control someone? Or at least to still be part of the Moon Guard?
Nevertheless I'd say that a mage mind controlling someone could be possible... but I'd say that it would be more likely that a priest from another race (one who is not affiliated with the Light) would possess that power.
The moonguard was the most elite group of mages that served directly under Azshara. Its highly unlikely that any of them would be remaining and not still be in her service in the depths.
There was other mage-guards though at the time, one would assume. Since magic was the goto weapon back in that age.
I don't believe the Moon Guard operates as a unit anymore; however with as long-lived as kaldorei are, there is nothing to stop you from playing one old enough to have been in the Moon Guard when it was still around. My own priestess of the moon that I RP is over 10,000 years old and survived the Sundering. Just do your research on the group so you are well versed and you can play as a former member, maybe one who still feels nostalgic enough to proudly identify himself as such.
You would be accommodating. At least to night elves.
Theirs is a culture of wariness of arcane magic... for good reason. They doubtless still hold the highborne in an uneasy light, to a degree.
Some arrogance would probably be there too... ultimately the personality is up in the air to an extent. There's just certain ways you'd want to handle certain interactions. Because roleplaying logic.
The important thing to understand here is that mage is a class, and mages in WoW are actually more diverse. Technically Necromancers and Warlocks are effectively mages. Lots of different types of magic are studied by different mages around Azeroth, the player class merely represents the best options for gameplay.
That being said, most types of mages hold magical control over other sentient beings whether they are elementals, demons, or murlocs. Azshara herself uses mind control, though that may be a power unique to her. It is notable though that Satyrs, Naga, and Blood Elves, all of whom were Highborne, use mind control. Many mages also use telepathy and other mental abilities. For gameplay purposes these have been applied to priests, but also note that there are many "Shadow Mages" who use shadow priest abilities. Therefore it is plausible that you can use some form of mind control. The question also becomes whether you are using possession (transference of your spirit/soul into another) or merely controlling from afar. The latter is more commonly observed, though the former is also plausible.
As others pointed out the Moon Guard no longer exists. It could however be something that is revived with the re-acceptance of the Highborne. You could have been in exile with the Shen'dralar or simply hiding amongst the fringes of Night Elf society.
The key to the character is that you were at some point a member of the elite, but you also betrayed that elite. The question is how does your character feel about that? Did they feel as though the other Highborne were the traitors? Did they always feel that the amount of entitlement the Highborne had was too much? Did they merely go with the flow and suddenly realize they weren't as special as they thought?
After answering that set of questions it then becomes about how they reacted to those events. Did they feel their people were justified in their anger and merely fade away to the fringe to let them cool off for 10,000 years? Did they persist in using the arcane but only minimally to assist their people? Did they go into exile with other Highborne?
Answering those questions will allow you to decide whether your character still thinks they are the entitled elite, or have gotten some degree of humility. Regardless you are likely to hold other users of magic, particularly the arcane in higher regard. You probably have some level of respect for martial skill too, though you may see non-magic wielding warriors as hamstringing themselves (pun intended). You may therefore find paladins and other magic wielding warriors interesting. Of course race may still matter as a Draenei comes from a more accomplished arcane society than your own and if you know or perceive that you will probably treat them more as an equal. A human rogue may seem like a mere flea though, whose combat abilities may be potent, but too short-lived in your mind to matter.
Anyway those are just some examples to help you, feel free to steal them or build on them or ignore them as you wish.
I don't see why you couldn't have a spell to mind control someone so long as you're reasonable about it.
Ban Reason: Blizzard doesn't care about alts. They said as much during this expansion.
Be wary of using mindcontrol in RP, though. Most players would not enjoy you forcing something upon their character like death, grave injury (or any injury, for that matter) or mindcontrol without their consent. So make sure you have that consent before proceeding.
Definitely would work.
Handcuffs can be fun as long as you don't get kicked off the bed and break your neck leaving your significant other handcuffed naked to the bed and no way to call for help. That's just no fun for anyone.
So actually I'm unsure of whether having a night elf at that age is viable. They're a long-lived race but I'm not 100% sure of their lifespans prior to the War of the Ancients and Nordrassil. Wowpedia's got it pegged that their adulthood is after several decades.