We are still thinking about what can be done with the current situation.
The main problem is the accumulating power of the player, which becomes ultimate over time, and we just have to change the numbers to challenge the player.
I'm sure the mode can be made more interesting, but I'm not sure what exactly should be done with it. In the background, I finished prototyping a new mode.
One of the options I'm keeping in mind is to make the current mode closer to roguelikes - change the spellbook to a "card roguelike" so that the player levels up and collects their deck within a single journey.
This will simplify the balancing task for me, reducing it to balancing within a single game run.