So the suggestions so far seem to be:
Nagash on Fulcrum assuming ETMagic (or SoM, if SoM fulcrums make casters immune to multiwounds, cannot remember). Certainly the most epic option, but that would involve playing ETM, which is... eeyrghsshsgh
Doom & Darkness plus Tbats/casket/banshees, with or without Nagash
TK shooting, with multiple catapults plus Khalida and a huge block of archers. I kind of question this as well, though, since franz is only on a chariot base, and not the huge base of our dragons/tgs, making stone throwers a rather unreliable option.
multiple
chaff units with champs plus invocation (an excellent option to tack onto other methods as a failsafe, since
chaff is cheap and you want to take some anyway)
IMO, the best option though is not to fight him at all. Call a truce to team up against chaos instead. All us good guys should be working together! After all, isn't one of the mortarchs an elector count these days? Nagash is practically an Imperial citizen at this point,
