find the fireball early without exploring too much
find the Jehora Jhiwatshisname altar early too, the Polymorph ability you can get from it is a must because both bosses are unkillable in normal condition by a wizard (one boss have way too much health and the other one has way too much magic resistance that makes your fireball make super small damage)
find a level 9 animated armor very early so you can skyrocket from level 1 to level 6 near 7 by hitting its death wards with fireball and refilling with fog exploration until it had no more death wards and its 1HP would then allow you to kill it with another fireball
find the 2 bosses , then once you have enough piety use the polymorph skill to make the 2 boss more spell assault friendly
if you're lucky and both new bosses are spell assault friendly, you then have a chance, and i was luck because i had then to face the ghost boss (that main point is having physical protection, so fireballing it wasn't a problem) and the goblin (that still had a few magic resistance, fortunately the additional mana potion i got helped)
buy any object that can help you with mana, i was lucky to have an additional potion of mana purchasable this time, good i had max gold because it was the whole cost too
ideally if you get the poison spell it's even better as you can prevent those boss to refill health in case you run out of potion/mana and must refill to cast more fireballs. I wasn't lucky to get one, fortunately the extra-mana potion i had gave me the win.