Not sure if you know this but you can heal the mindflayer
My strategy relays on shadowheart
Enter room
Cast shield-shadow heart
Rest of party wipes out minions
Then potentially shoot from range(everyone gets a bow or crossbow)
Potentially heal mindflayer-second shadow heart spell
Keep on eye on its health. Worse case shadowheart throws healing potion at it
Take the cambion down with plan that him and mindflayer are 1-2 hits
Your bard should buff laezel
