Thanks for all the pointers! I used my reflexes and DP against Gharbad, although TT didnt like that. So maybe PISORFing him to death without touching anything else is a good strategy. Especially with B2P opening the tiles right next to me, he should not regenerate in between... there are a lot of small things I can still optimize, but wow the difficulty is really high
For preps: I use Fortitude, Reflex, Quicksilver and Strength Potion, Fine Sword, Perseverance badge, compression seal, more glyphs (to have better glyphs overall and the reduced conversion actually helps in reaching the threshold. Then one extra shop and black market to have a good pool and more money in the second part to buy everything I want. I am pretty satisfied with that right now.
But yeah, probably next time I reach the final boss chamber with all these added knowledge, I should be able to defeat him... we will see I keep you posted