A few days ago I was joking with someone how I intentionally didn't include Wyll's potential evil epilogue ambitions into my original post because Wyll's just a nice guy. I truly have no idea what Wyll's evil ambition could be, other than probably becoming Karlach's ULTIMATE EVIL sidekick yet again as a joke. But in all seriousness I personally saw his ambition and motive as;
[color:#CCCCFF][list][*]Him becoming so fed up with Mizora he eternally imprisons her to torture her and then becomes so consumed by hate against devils he fully embraces becoming the actual vengeful Blade Of Frontiers from Early Access, paying a visit to the Hells and slaughtering the devils with such brutality he eventually fully evolves into an archdemon himself by the time he's done. Ultimately becoming the very thing he hates.
That is a great idea! I think (though I am not quite sure if I remember correctly, would have to replay the scene) this is even one of his magic door answers in act one: to humiliate Mizora. And Wyll becoming a sort of vengeful antihero would be amazing, because: whoever fights monsters...
Frankly, considering Mizora gets the sort of plot armor protection in act three not even main story characters get, I believe she is the writer' 'pet favourite'. So neither the player or Wyll are allowed to get revenge on her, not even after obtaining the ultimate power.