Crazy idea: What about having Adaptoids and Symbioids as an available character?
Alright, I know I sound insane, but hear me out. This just might work.
Acquiring these champs:
At level 5, 15, 25, 35, 45, and 55, you would get an Adaptoid. The first would be Skill, then Science, then rotating all the way back to Mutant. You could pick that champ's SP move and then one Passive ability from that Adaptoid's class abilities that are used in quests. This would be the same for Symbioids, but would be on levels 10, 20, 30, 40, 50, and 60.
Ranking them up:
When you get the champ they would be a 1*. You would go through all the ranking and leveling, then you would be able to upgrade their tier to a 2* for 5 Tier 1 Basic Catalysts and 5 Tier 1 Class Catalysts of whatever their class is. Once you max them out as a 2*, they would be able to become a 3* for 5 Tier 2 Basic Catalysts and 5 Tier 2 Class Catalysts. This would go on and on until they were a 5 star. The tier of the catalyst would increase by 1 for every star upgrade. This would make it insanely hard to make them a 5*, so new players wouldn't be able to pick up a 5* quickly. These Adaptoids and Symbioids would progress in ranking as you do. Due to the expense of ranking them up to the next tier, they wouldn't be many people's top champ unless they just did nothing to anyone else. They would be a fun background champ to use for quests and arenas. Plus, Adaptoids and Symbioids don't have SP3 moves, so they wouldn't be too reliable.
Overall, these champs would just be a fun new concept. They wouldn't be very good, but would be consistently decent since they get better as you do. Let me know what you think in the comments! Thanks for reading!
-CrusherOfDreams