Perhaps I'm not familiar with all kinds of Mephisto moat tricks, I know for two where you either trap Meph to the left over the river or on that island where is portal so you shoot at him from distance. Both are presented in first few videos on youtube. Is there some faster variant of moat trick?
For those two variants you have to get to Meph, or at least at the centre in front of him to drag him down so you can tele over the river to start killing him. First part is exactly the same thing player does using merc, but instead of teleporting over river and waiting for Meph to come close, he instead starts killing Meph right away using merc as a tank. In time user of moat trick starts killing Meph, player with merc as tank already took half, or even more hp from Meph. That is reason why moat trick, at least those two variants I know of, cannot be compared to direct killing Meph in killing speed.
Blind spot of Blizzard... I must admit this is the first time I hear about it. Even if that does happen, it's incredibly rare. I guess you still finish off meph with ice blast very fast.
Here in second post are presented some results of how fast is possible to run Meph and with what equipment to be "perfectly safe" from Meph without using moat trick. As for moat trick... I know I can't really come close to 25 sec range running time using moat trick, but I'm interested to see others try to do it that fast. Or faster.
To answer question, I namelock Meph with Blizzard and just throw. No science there. Sometimes it hits a lot, sometimes it misses. Strategy is to throw blizzard, then spam static field as Meph is approaching you and your merc. Get him down to half hp, then just blizzard + ice blast him to death. Moat trick is great for weaker characters who are undergeared to take on Meph directly with merc. Perhaps it is possible to run him faster with moat trick, but I don't have knowledge about that.
Also, just for a note, fireball sorc using infinity merc is by far fastest Meph runner, but then again I'm not sure why would anyone who has Infinity run Meph excluding farming essences. Still, if someone has a reason to do it, try it.