So, the most important thing you can possibly do to kill a muter is get his ####ing staff out of his ####ing hands.

Like all mages, even hasted and you slow, he'll die like a bitch without a weapon.

So any strong maledicting class combos are going to be hella dangerous for a muter, especially classes like Warrior (dagger spec)/ Druid/Shaman/Necro/AP who can drain their mana/regen.

That being said, classes like ranger/thief/orc (assuming noremove staff)/bard*/paladin/shifter/invoker (assuming no needle mals + immolation)/conjurer*/healer** are pretty much meat for a transmuter who knows what they are doing.

*Edited to add: These opponents play slightly different in PK, in that with conjurers you often go ALL DAMAGE and with bards you can use spells that drop their charisma and potentially prevent them from singing.

**Second edit: Healer is meat because YOU have so many tools to drain his mana. And a healer without mana is a dead ####ing healer. Paladin is SLIGHTLY similar if you find yourself unable to match them in melee. As is any insanely geared invoker/shifter. FWIW Healer is the one class I'd keep a nice exotic (or poisonous dagger) on hand for because of options with maledicting wands.