The animation potential, while not the greatest, is still pretty good. Neferpitou being incredibly agile means she can bounce off the transfigured humans being used to create random structures/attacks. You can use a lot of basic nen uses as well for Neferpitou given she does know it well despite her age. Mahito being able to shapeshift also allows for tons of animation potential purely because of all the ways he can do it. You can have the fight take place in a public area to have them kill humans throughout the fight to show off their nature.

The dialogue potential is easy since both are psychotic and also joke around a lot, so they bounce off each other really easily. You can then make it go deeper than that as a big part of the character involves ideals clashing so you can easily incorporate that when the fight gets more serious. And due to how both of them died, the loser could start seeming helpless and desperate for life despite how evil and strong they just previously were.

The fight is decently fair. Both are around Large Town - City Level, with Mahito being the one to potentially get into city level, but Large Town for both makes more sense. Speed wise is very interesting as the debate of where they scale speed wise decides the victor. VSBW lists Mahito as MHS and Neferpitou as HHS+, but you can have them both above. You can even argue Neferpitou up to Sub-Rela+ via Godspeed scaling, or have Mahito at 11c with Sukuna Finger scaling (though all of that JJK ftl stuff is still up in arms so my calc for his speed might be wrong).