i recently finished doing it my self for the sacred, and i can tell you this much, artak is able to solo most of 12.

also on 12-7 ur always going to go through a bit of a coinflip, kinda need to hope mortu doesnt peril you, might take couple attempts.

try klod and artak or something, might do it since i think most of 12-7 is green affinity

Because you dont have Paragon, cant using Paragon cheese strategy. But I should try Ma’Shalled paired with a very slow and very low hp Gnarlhorn with 2 turn stone skin set.  (Keep it lvl30) If stoneskin end you can use 2 turn unkilleable skill on it.