In Krowly's laboratory, you can access a cheat room by interacting with the bottom right square. On the right wall of the cheat room, there's a boobed Krowly you can interact with to toggle Krowly's boobs. While Krowly has boobs, Krowly should have an item that toggles whether or not their outfit shows cleavage.
There is a quest that entails you creating a boobs potion, you have to do a number of quests beforehand. After doing that quest, you'll also get a quest to learn how to make a boobs reduction potion.
