I've always been of the opinion that Bell will solo Udaeus for his Level 6 feat. Nothing could symbolically prove to him that he has achieved his goal and reached Ais's level better than duplicating her most famous feat.

A full developped Minotaur Demi-Spirit to serve as introduction for the main antagonist of Ais Arc. His howl also inflict not just fear but also multiple status effects including charm but maybe it would a too easy fight for Bell.

The Behemoth alternative, If Omori decides to adapt the story of the Great Day for volume 22. Bell deal the final blow & also survive being exposed to a massive quantity of his poison.

Solving the issue with Juggy-peluda, it's mostly Bell beating him up & talking while he recovers repeatedly until Bell finally finds a way to coexist. It took several tries & visits on the 37th floor with Bell & Juggy improving over time, the last duel was the 73rd with both of them becoming much stronger Juggy from eating magic stones & mutating like Asterius did in his previous life because Ottar while Ais finally fufill her promisse to train Bell but Ryuu also involved herself like she did for training with Hedin.

A level 6 Phryne who got cheat skills & curse (charm type) consequence of the trauma inflincted by FF executive, coming back to take revenge on Bell. so we can complete the 3 duels against her serving as mirror between Bell & Ais (1st: Defeat, 2nd: Draw, 3rd: Victory).

Defeat Cadmus in an expedition with FF on Floor 50 & below. This would be a greater feat than simply repeating the solo Udeaus fight for the 3rd time in the series.

I was hoping for a joint expedition between the Hestia and Loki familias in relation to the info given by royman, with some Freya familia members so that the Hestia familia wouldn't be so reliant on the Loki familia as a crutch.

Thinking about it more, I feel as though it would be awkward and unwelcoming between both familias on said expedition.