ColonelHardisson
What? Me Worry?
I rationalize the Mouser at being around 21st-22nd level, while Fafhrd is around 19th-20th. The Mouser I envision as having lots of rogue levels (naturally), and at least a few monk levels (which would account for how he could be buried alive and not only live but move). This is assuming a period from later in their lives, in the stories Leiber wrote near the end of his life.