Yo, how hard is heroic mech, i really want that sun eater and also what is a good group to take with is 2 mages a must ?
Probably the easiest heroic in the game. It is recommended you bring a warlock for the 4 demon-heavy pulls, and if they're affliction and have instant Howl of Terror, that's even better for the final boss. The first boss and 2 minibosses require no special group compositions, the 2nd boss you're better off with a healer that can throw hots instead of having to channel heals, and the 3rd boss like I said, the instant aoe fears are helpful.
A good setup for the run would be warrior/warlock/healing priest/mage/rogue but to be honest you can usually make any setup work there. If you want the run to be smooth though, you really should bring at least 1 real cc besides the warlock, and the healer will be way less stressed if they're capable of throwing hots instead of channeling all their heals.