Slight optimization - start with a pet that has Feign Death. That way you only lose one round to the clobber instead of two and there's no chance of your valk dying and therefore missing haunt. Also, for the pet after Haunt, I use a Macabre Marionette with Dead Man's Party for the double damage debuff but there are many options there that would work just fine.
I found this strat on the web and used it. It worked like a charm. I used it for all 3 boss fights. Two turkeys. Peck and Food Coma. Food coma > switch turkey > peck, food coma > switch turkey - continue until the boss is dead. Turkeys take no damage at all because the boss is constantly stunned with food coma.