Strategy 1 - Salon Cat and Valkyrie Cat
To beat this level, use Salon Cat or her evolved form, Paris Cat. Spam as many Salon/Paris Cats and meatshields as you can. When the base is around 50000-60000 health, St. Pigge the 2nd will spawn with the boss, Gory Groom.
When Gory Groom and St. Pigge the 2nd spawn, summon a Valkyrie Cat. Spamming meatshields is a must, as Gory Groom can easily kill True/Holy/Regular Valkyrie Cat and your Salon/Paris Cats.