Glorious evolution

On higher difficulties, pinkies are more likely to transform (into either blue or orange). Floor 1 is ideal for catgirl to attempt this.

Similarly, on higher difficulties, oranges are more likely to transform into sunny. Catgirl should head to floor 3 for this.

While on floor 3, catgirl can shoot a blood bullet at sunny without moving (without starting the timer). This will evolve sunny into sunkensunny. 

Catgirl does not need to defeat sunkensunny to get this achievement.