I mean, they literally can't make it "difficult" the worst thing they can do is make it kill aminon.
There's no shot they can make it kill all 9 bosses in one run etc
(it's not "impossible" just unprecedented)
Difficult in the sense that not everyone is killing all bosses so it will be difficult to complete all of the objectives. A lot of people haven't cleared all 9 bosses, much less all of them in one go.
I expect these objectives will all be tied to each respective NM/Boss. Maybe +1 cases for top floor and +2 for basement and Ami?