How to Beat Commander Zhalk
This would actually depend on who you chose what methods you can use overall, if your have access to protect from good and evil on your character/s that’s a fantastic spell to cast in the mind flayer, if you can hit the devil with any spell that causes advantage for you or disadvantages for him for multiple turns, like Hex or fairy fire.
If you have high Str stats, grabbing all the purple containers that are explosive on the way that you can possibly hold, with enough you can insta kill both, or just do very heavy damage with a few, you place them right next to them and boom! Preferably with a fire dipped arrow and everyone on the button side lol.
If you have a ranger or anyone bult for long range with bows, get up on the back rafters area and you get a slight bonus to hit leazel is actually decent at range herself and i think she has a bow. This should make it better to help hurt the devil.
Once you get use to it, it becomes quite easy with any character choice, but you may have to try several times, abd you absolutely do not need the cheesy methods to beat it but they are options.