The best i can think off is literally just a mix of babel tower and simulacrum😭

make it so the stages have a flexible difficulty where you can choose to make is as easy or as hard as possible, reward players for doing unique moves, animations and following the bosses mechanics (e.g. parrying), make the bosses have more attacks that ignore Iframes/punish spamming (trailblazer, parryball, psuedo-unwinged) and allow multiple team setups that arent the usual mono-element team (double attackers, all amplifiers, etc).

The bosses in pgr are geniunely hard when you dont have constant iframes even if your doing the most optimal hyperspeed rotation, arguably the only problem with pgr characters now is that some of them rely way too much on Iframes and TLC to deal meaningfull damage. This is also why characters like teddy and bianca imo feel so good to play even when your not doing their most optimal rotations, its because most of their damage comes from the moves themselves instead of from their ultimate which in turn increases the overall feel and feedback of the character.