If this mob feels like fearing itself for a particularly long time you will wipe and there's nothing you can do about it. Just bring extreme dps and pray it's first couple of fears break early.
The enchanter spell line "Compliant Lurch" (I, II, III) can be used to keep Maddened Mephit from running too far away while it does its running-training-aggro thing. It will likely repeat its run-away attempt several times during the fight, so be sure to re-cast Lurch before it wears off.
Just before the mephit does its run, it knocks everyone back into the air slightly, using the spell "Repulsive Force". If the enchanter who is lurching it gets too far from the mob during that knockback, the leash will snap and you will have a huge train on your hands. Be sure the enchanter runs back to the named immediately to re-leash/lurch it.
[Tue Jun 29 03:20:39 2010] Maddened Mephit begins to cast a spell. <Repulsive Force> [Tue Jun 29 03:20:39 2010] Maddened Mephit shouts 'Aaaaaaaaaaaeeee! Oh my, oh me! This is terrible, I must flee!'
[Tue Jun 29 03:20:54 2010] Maddened Mephit begins to cast a spell. <Infectious Madness>
Note that while it's doing its running thing, it memblurs itself and becomes non-aggroable. Once it stops running, it reaggros. So if an enchanter is leashing/lurching it, the tank should ensure to grab aggro back right away after the leashed run ends.
I was told that some kind of Beastlord Pet-related Snare can also be used in this manner, but I do not know the details of this ability. Shadowknight's Hate's Attraction is usable for this leash as well, but the reuse timer on that ability makes it difficult unless you have lots of DPS with you to burn down this NPC before it runs away a second time.
Also, it seemed that we could pull this named from among a crowd of other mephits and golems without any assistance from them. So almost no clearing is required, if this NPC is already up. It appears that the other non-named mobs are non-social with this named. However after a (non-leashed) run, the named appears to either aggro nearby NPCs, or you as the player aggro the NPCs if the named summons you to them.
just tried it today. SK, ROG, NEC, BST, DRU, CLR, and 2 CLR mercs. had a good fight going till he charmed us. then he started running away and I [being the sk] used hate's attraction aa to get him back to us and keep fighting. was going well from there till he did it again and ran around corners. we lost him till he summoned us to his loc in the middle of a bunch of cliknars. of course we all died, only getting him to a little less then 50% hp.
this mob is horrible...the only thing I can think of to kill this mob is to clear the entire area where it spawns, and burn it down before repops happen, so you don't get any adds.