I'm very confused by this. This week's event is to kill the Undead, not Monsters. And Alchemist isn't a monster, so it wouldn't have a place on your team anyway.
For what it's worth, though, I've used this team for defense in the past:
Double Red banner
I like that any troops that do targeted damage will target the weakest enemy troop. Saves me from worrying about the AI making boneheaded moves.