Cleon
Legend
Whenever that's updated, how about CR 3?
My thinking is this is one of those monsters with a very "swingy" Challenge Rating. Basically, its CR depends on what magic items the party has.
CR 3 seems a reasonable ballpark for an incorporeal creature with its Power Touch attacks and myriad defences.
Hmm, it might even lean towards CR 4, depending on the likelihood of its PC opponents being loaded down with magic items for the Tarsardar to turn against them.