My Freeze Merc does great with the following gear:

Sazabi Armor - I dont know why but this seems to work better then any other armor ive tried including shaftstop.

Crown Of Thieves - Etheral, great Life leech.

Brainhew Ogre Axe - He got lucky cause I found an etheral one, but regular one works great too.

This merc can go toe to toe with Meph and kill him in about 30 seconds with very little help from me.