Is it intended that there is a chance for the Nemesis to not even be in your Mirror Temple? Because I think that is very silly if so.
Otherwise I think this is a fun addition, very neat to have class-specific challenges
Also, what is the reasoning behind the Uber Butcher requiring an Urt rune? Seems really weird to gate it behind an item at all, much less a very specific enhanced rune rather than, say, any enhanced rune.