Francoise + mandrake makes it a cakewalk. The key to winning is not enduring the fight (unless you maximize your ideal heroes, you will always lose in an endurance battle), but blitzing Kurtz. Right before the last enemy is killed in wave one, start pumping Francoise’s silver skill. After the dialogue, once the skill is loaded up (level 4), pass it to mandrake and target Kurtz. He should go down in 3-6 shots, depending on your heroes’ strength.