u/R0DAN

Apparently each character has a "true" final boss, but I have no idea what gets them to appear

It seriously has everything I'd want in a sweaty single player mode. I love that each character has their own intro, midbosses and final boss. It shows a level of care that I didn't expect. On top of that the gameplay is just so addicting, I'm a roguelike fiend and so this mode is scratching that itch really hard. Each run feels like a progression on the last because the CPU can be absolutely brutal, it is a very sweaty mode and so you need to do a few runs on each character before you can alleviate that a bit. The fact that it has metaprogression and extra things to unlock through simply playing the mode a lot and beating it with many characters is genuinely so addicting. I could see this consuming my life for a while lol