Yes, /Emp is generally very tight. That being said, I don't really recommend /Emp for you. It really depends on what your buddy is going Demon/???
If he's going with a secondary that has a heal, there's really no point for you to go /Emp.
Regardless of your primary, I would recommend going /Kin, for good ol' Fulcrum Shift. Fulcrum Shift + a bunch of Demons? Sounds fun to me. In fact, the only 2 secondaries you may want to avoid is Empathy and Storm. Although, Storm may work for you if you don't mind mobs flying all over the place and henchmen chasing them everywhere.
Thank you for the advice, that's exactly what I ended up doing. My buddy loves the Ice/Kin I have on red-side, so he asked if kin was possible. So far I really like mind. The big draw for me to empathy was the fact that I had never played it before. I think hes planing to roll up a Demon/Dark when the expansion hits and take him blue-side. So I'm going to level this guy up to 20 and then try Mind/Emp on a alt.
I have never rolled a blue-side before, but I have to say its pretty fun (well aside from not having any infamy). Thanks for taking the time to reply to this thread I appreciate it.
Edit:How is the mind/psy dom? I've never had a chance to get very far with a dominator.
Mind primary is a ton of fun I don't know how I missed it for so long!
I disagree with the previous poster. Any secondary will work.
The only reason to avoid Mind/Empathy, potentially, would be that you don't have a pet to heal or buff. That's a big deal to some people. To me, buffs are only as good as the pet you're actually placing them on, so Mind/Empathy is just fine.
Whether your teammate has a heal or not is really not relevant overall.
IMO if you still want to play Mind Control and want something that meshes well with your buddy, I'd recommend Mind/Radiation. /Kin anything is just fine, but IMO more difficult to play well.
I've been playing a mind/emp recently and it's a very good team character. I'm much more with Tex on this. Even if your friend has a heal in his secondary, Empathy is much more than that. Fortitude is an excellent all-around buff: a bit of damage, very nice tohit, and respectable defense. It gets even better with Primal Mastery as you can boost the defense to around 30%. In fact, the heals have played a relatively small role in my experience with mind/emp. As a team-oriented character mind/empathy will do very well.
As a duo, however, I'm inclined to agree a bit with Spine but for different reasons. If your friend is a bit rusty or unfamiliar with commanding MM pets they can interfere greatly with Mind's controls. For example, you may take a boss out of the fight with Mezmerize only to have a pet slap it awake. If duo'ing I would probably also favor secondary with more AoE debuffing. It's easy for the MM to buff their own pets due to their interface, but might be a hassle if you try to do the same.
I'm a big fan of Mind/Kin, have run several including a duo where my wife and I ran a pair of Mind/Kin and just steamrollered just about everything in our path. 
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That said, I'd say that while Mind/Kin will certainly be a killer combo with your friend's Demon/?, one of the downsides you will have is the lack of an Immob to lock the spawn in place and keep your friend's pets from running all over chasing the mobs. So that's something to consider.
OTOH Speed Boost will bring up your Demon summoner's Tar patch a lot more frequently, which will certainly help with that. If he goes /Dark Miasma it could be a great pairing because you can heal the pets in melee while he heals the pets near the two of you. I've noticed that one of the major limiting factors for the tier 3 demon pet is endurance usage, so a Speed Boost with 2-3 endmod slotted will probably turn your partner's demons into... err... Hell-on-wheels? .
Obviously, once you get to 38 and pick up Fulcrum Shift you two will just mow down everything in sight.
If you're interested and willing to play a really ACTIVE character, Mind/Kin will be highly effective for you. Esp since you will be able to sleep a spawn, have your friend put his pets on defensive and all run in for a FULL FS boost before the fight even starts. Mind/Kin excels MOST on well coordinated, disciplined teams, and an good MM brings THAT to the table in spades .
Oh, and Mind/Psi is an excellent combo. It used to have a BIG problem with single target dmg in the late 30's and 40's when you start running into EB's every other mission (EB's are a real problem for Dom's due to the Purple Triangles of Doom allowing them to basically ignore controlls for 2/3 of the fight), but the major rebalancing of Doms helped out with that quite a bit.
Drain Psyche is a set defining power that makes Stamina pretty much irrelevant, and can make you regen like a /regen scrapper in the right situation.
One of the problems with Mind/Psi, is that almost all your dmg is /Psi, which is HIGHLY resisted by groups that become more and more common in the late game. You need to learn to use Confuse to make the non resistent mobs kille the psi-resistent mobs FIRST . On the flip side you'll tear through CoT Spectrals like they were tissue paper.
I play a Mind/Emp--she's my only 50 so far. She's really good especially in small teams like a duo, so usually I'd back up that combo for a duo. But I agree that it's probably not the best combo for playing with a MM--in my mind the duo partner that'd gain the most from Emp would be a squishy (or a scrapper/brute/stalker that isn't built to be indestructible).
MMs don't gain nearly as much from you buffing them, since they tend to be tough already (and one with Dark Miasma can heal themselves pretty well as well as debuffing tohit), and they have very little use personally for +damage. So Fortitude only benefits them so much, and it's a huge pain to buff others' pets. I never bother even if the pet would benefit more than a given teammate--I can't tell its status at all and targetting it's more annoying unless you create a special targetting bind. Hmm, I might try making that bind.
Depending on the secondary, they could benefit from +recharge and +recovery, but you'll get that on them far more reliably with a Kin--unless you spend a fair deal on +recharge set bonuses. I did and I don't regret it (nearly perma Adrenaline Boost is tasty and it's nice having other stuff come up a lot more), but not everyone'll want to. And you probably aren't looking for a major investment. Oh, and as an incidental note pets don't benefit from +recharge at all--they're immune to recharge modifications.
Mind/Kin should be good for the reasons already stated by others. It goes really well with anyone with a lot of damaging pets, really (except Illusion).
Mind Emps can be very busy, if you proactive buff that's a chunk of time gone, should you controlling instead of buffing or buffing instead of controlling? There is always one or the other, every power you use has a cast time and for the moment your locked out of using another power.
Prioritizing correctly as to what should be when is something that's rivalled by other peoples ability to be unpredictable. Quite frankly I give it to people that I made a controller, not their buff bot, I'd sooner people played with mobs under control than shoot in and need healing.
I know it can be best at times to buff someone else for the pace but sometimes you end up with some lunatics who think thats the case with their characters plus I normally don't like doing some empaths job who seems to think they are there to sit back and spam heals when needed asap.
There are Mind/Emps doing their job and that of the defender but people can't expect too many operations to happen at once, every power has a cast time and Mind/Emps will have to prioritize. I take it that due to the amount of control Mind/Emps can have overtime the Emp side isn't that important if the team aren't gung ho. Mind/Emp players just don't mind read. /Empathy is much easier for control sets with pets, especially illusion, because the control side of things is pretty much being taken care of, and so is the damage side. Mind control can make things smooth and easy, using Mass Hyp but some people like to wake the world and his mum up with fireball and then expect heals.
He will honor his words; he will definitely carry out his actions. What he promises he will fulfill. He does not care about his bodily self, putting his life and death aside to come forward for another's troubled besiegement. He does not boast about his ability, or shamelessly extol his own virtues. - Sima Qian.
Well. The thing is Empathy supports the Mastermind as a Tanker-mind. If the Mastermind has Provoke, and you Fortify him/her and his or her sturdiest pet, and Regen Aura the group you effectively have one of the strongest tanks possible. The Regen Aura is 5 to 7 times more effective than on a "real" Tanker because its hitting more targets, and net gain in Regen is FAR higher than it would be on a single character, for the same endurance cost and cast time. The only powers that are less useful, potentially, are Recovery Aura and Adrenaline Boost, depending on the MM's secondary. A Storm, Traps, Trick Arrow, Dark, Poison, or Thermal MM would benefit rather significantly from AB due to the huge Recharge boost speeding up power availability. Force Field not so much, but I can't think of the last time I saw a FF Mastermind, and in that case you could simply place the buff on the best pet. The thought of a big Bot with massive Recharge is kind of frightening, actually.
[EDIT: Strike that, forget pets are no longer affected by Recharge buffs. But, everything else should still be true.]
I have just returned to the game, and I am totally new to blue side, so I thought I would come to the forums for some advice. My friend plans to return for the expansion, and plans to roll some sort of demon summoning. While looking at the possible characters I could roll to go with his MM I came across the idea of a Mind/Emp.
The problem is that I know absolutely nothing about controllers, the mind power-set, empathy, or the blue side patron power pools (leaning toward Primal mastery). I have never played a dominator either so my experience is very limited. I read a few guides from i11-12 that covered mind and some that covered empathy, but it was hard to get a good idea of how they would work together. I rolled one up and am currently leveling it, but I don't want to get very far into it so as to not ruin my experience with leveling it up with my friend.
I messed around with the build for quite awhile in Mids, and to me it seems like a very tight build, at least, if I am to believe what others say are the must have powers. I would really appreciate it if someone with some experience with this combo or even these power-sets in general could give me a few pointers. It seems like it would be strong, but even if its not the greatest it fits the type of character I want to make. The closest thing to empathy I have experience with is a Energy/Thermal on red-side.
Thanks for any help you can give me =)