Are you CL10? If so, you really don't have a chance (voice of experience), but OK...
Buff up in Null. Everything ya got (better all be CL10 / RR4).
Amp.
Go into first area (where Alastor is)
Zip through there...you can't attack anything without being mobbed
Go into the next room.
Go to the left ledge
If you're lucky (the monsters rotate positions), you can get to a point where you can nail just one, and then duck back when the heat is too much
Repeat until you're dazed or you look at their health and realize they're healing faster than you can damage them
I have tried this a few times hoping I could get at least a few shadow orbs, but the most I've accomplished is feeling like a little raggedy grrl being patted on the head by a giant werewolf and told, "Oh, look at those tiny little fists! Aw, you're so cute. And tasty. ROWLF!!!" before I ran back out.
If you're above CL10, I think you might be able to solo OK like this, but I doubt you'll get past the first two rings. Probably best if you have at least one attack at 12, I'd imagine.
I hope this helps. Otherwise, DMS needs a crew...the monsters really are that tough.