levels 1 to 2 are really bad, with level 1 being a battle field, the town of beginnings in ruins an always on fire.
levels with elden ring bosses, to Alduin from skyrim.
a dimensions that is just Aincrad, and every other show an game and everything is here. this is a physical world people are stuck it, by some strange mad god at the top of the level. stuck. for the fun of some evil god.
other bosses are
Pyramid Head
Bowser 
Dark souls
General RAAM
GLaDOS 
level 3 safe zone. many characters there