As I keep pointing out, defeating the demon lords takes a long time, but it isn't really all that difficult, as long as you are prepared.
Make sure you're at max level, max HP/MP, and have meditated at the bath. Stock up on all the potions. Maybe think about what skills you're most likely to need and adjust them as you see fit. Some recommend you enable the MP drain skill (gainable by wearing the succubus leggings for a while), but I've never found it necessary.
Start by attacking with your single-target spells. When the side demons appear, use the multi-target spells.
Use the invisibility potion and get some free attacks in. Use the health and magic potions when you start to get a bit low.
When the demon grabs you, don't struggle out of it immediately. Let her play for a while and use that time to recharge your spells. The allure potion might be useful there.
Whenever its available, use your Celestian form; particularly the time-freeze, which gives you five free attacks. When you get defeated in that form, you are simply back to your previous situation. When it has recharged, do it again.
Just keep attacking until their recharge ability runs out, at which point you'll finally be able to defeat them.


