After trying out all classes , i find this below is the optimal class bear cdr zhalk easily :

- start as War Domain Cleric , that will give you extra attack per turn for 3 turn , STR and WIS and CON primary stats
- set Bane as prepared spell for your cleric , command and bless for Shart
- before entering the final room Bless party using Shart and then click the blue energizer thing to recharge spell slot
- enter the room , dash Shart forward to command zhalk to drop weapon
- Shart take the dropped weapon and to your cleric.
- use your cleric's bane on zhalk
- move forward and you can demolish zhalk with 2 melee hit per turn for 3 turns

OPTIONAL
- Pick empty chests (total 3) to block the passage way to zhalk's room so cambions cant enter room
- pick purple canisters and drop them around zhalk and flayer , explode them all and then hit the survivor with your sword