I want to start off by saying that I suck at explaining things and I have a lot to try and explain already so if I miss anything or if you just need some clarification, please feel free to ask. I'll gladly answer!
Think of this like a combination of Madoka Magica Portable on the PSP gameplay combined with exedra battle system.
So for the mode, you would descend down floors of a labyrinth until you got to the witch. You would only have to go through 4 floors max. Each floor would be a 5x5 grid, have small obstacles and also minions. You would move your character with up, down, left, right and as you moved so would the minions. Each floor would have 5 doors. 4 of the doors would loop back to each other while the 5th is the exit. So it would be A¹-A², B¹-B² and then C. A and B will never loop into each other so if you went through A² you wouldn't come out B¹. You may also need to finish a different objective for each floor. One objective would just be "find the exit" while another could be "beat all minions". As for the battle system, when you come into contact with a minion, it would be like the story mode and start the fight.
I don't think I left anything out but if I did, I'll edit this accordingly.