*lol* diabolos is hard without a good setup...
I will say this though... dun...use...a nin tank...
because he has a move called netherblast which is ranged and ignores shadows
...plus, a pld is essentially better with their higher than average defense
and their ability to cure (...to wake ppl from nightmare.)
a rdm is also essential... for chainspell stun.
as is Blm since Blm nuking seems to do about 30-40% damage to him
there's a method one can use to fight diabolos and and still have the mages remain at the top to nuke/heal.
but the pld has to disband the party first drop down
and then be re-invited by the leader after getting aggro by diabolos.
the draw in won't take effect then.... at least not at first, which will allow the mages to safely nuke out of range of nightmare.
...however if... a blm overnukes...
and gets hate. ...you will be immediately drawn in.
so... gotta be very carful and exercise a lil control...
the nightmare move is definitely to be feared...
but from the top ledge (from where you drop down)
the mages will be out of range from it.
that's the safest method if you ask me