Ruins of Amdapor Diablos Guide

[Yumi_umi]

If u have high hp 5k + an use stoneskin u can negate nightmare ( falling asleep )
Also just designate the healer on door duty.
-open 1 door preemptively so that later when he charges u can easily open the 2nd door and have lots of time doing it.
-once u the void appears the symbols on the doors will light up again, this will give u a chance to look and match any doors u missed/ forgot.
Doing this tactic will allow for maximum dps time as both dps and tank will be constantly attacking diabolos. So u should be able to kill him after the 2nd big aoe.

[SpookyGhost]

If u have high hp 5k + an use stoneskin u can negate nightmare ( falling asleep )

And if you have less you can Stoneskin + Tank LB1/2. Did it our first attempt when the healer forgot the color combo for the last doors before Diabolos died. :P