Master Illum  

Master Arcania is in the 'magic' section of Sepulchre East. That would be the 2nd down from the north or 3rd up from the south. The southern one is Lunayan and the next is Kolos. you want the one north of Kolos. Its the area that reminds you of Alra, with the 4 different mob colors / factions. light dark nature and arcane. Now that you are in the right section, the ph's for Master Arcania are [ Arcane magic caster ] and [ Arcane magic wielder ]. There are 3 of them. note there is no "an" before their name. The trash are an_arcane_magic_caster so thats how you can tell which are phs. One is on the platform towards the back near the relic and 2 others path on the north side between the light platform and the arcan platform. Master Illum has 3 phs, but they are the Light magic caster types without "a" in front of their name. I will post this info under Master Illum as well.

Casts debilitating light PBAE that is a minor dot, then manifests either as a slow push or slow pull. Not sure what mechanic determines which. Back tank into a corner.