Ive seen some teams using Drexthar because of his passive and although risky it can work but not realiable. 

i

You need constant Dec Speed procs. Adding a cleanser or block debuffs is a good idea.(all of these are done on Void.

Geomancer is obviously the best choice and getting him is easier since all you need is support champs with dec speed(Stag KNight, Scyl[a2 off] to name a few).

i

Having some High Brimestone Champs especially the free support champs like Loki, Adelyn and Skeletor can help a ton against the boss.

Im curious to know if anyone has tried pure dps strategies against the boss? I rely on slow burns and tank the damage. Can pure Brimestone work? I dont have any Unkillable and Block Damage so if you pull those (Helicath, Demytha, Roscard) good for you

i

Alice can be a potential solution to climb some floors. As long as you have good support to keep her going. Having 1-2 Champs in Brimestone can have you skip turtle strategies and speed up the run somewhat.

Post your interesting build ideas to tackle this boss