There is no only one “proper”/more effective way of damaging the main “core” during the brief periods that it’s exposed. In this guide you’ll find some of them.
Tips to Beat Final Boss
To kill final boss you can use the time slow and gatling blitz to do decent damage.
Gatling Blitz does do pretty decent damage on the core if I happen to have it charged up, but I’d prefer to save that for the Angel Illusion form, which Lola confirms its strong against. Especially once I try to aim for the hour-run achievement.
Cryo-Flash’s time slow even work on the core in any capacity. time slow works, give you more time between the blasts that home in on you. it probably just doesn’t do much damage to the core.
If you have the upgrade to be able to launch the razor wheel on your third melee strike and know where to stand and time it right, you can launch the wheel without it going too far away to stop doing damage, and use that time to dodge the incoming projectiles and get into position on the other side to repeat the process without any downtime on doing damage.