If your looking to get this solo, here is an easy method. You need to get 500 damage in a combo.
Load up level 5, I used blaze, underground and gather the stars through the level until you get to the boss after the bar. Once you get to the boss wait until there are a few enemies about and then unleash your special star move, wait a second and unleash again until you have combo’d all your stars.
I left a video showing how I did. You can see I mess up my first star but still have enough to make over 500 for the combo.
Star locations
First is toward the end of the underground part, just before you get to lions.
Second is in the bar if you smash a chair. You can grab the third by using the taser on the arcade machine and it’s in the retro level.
There is another if you smash the motor bikes in the yard