SPOILER
Don't forget to Breast Expand mother of orb demons after you collect all 3 
They get attracted to Boobs 5+ (you start with Boobs 2 and Boobs 1 minimum) but they don't lose attraction even if you got deflated by enemies as long as they didn't lose you.
Also don't forget to breast expand rabbit after race, You can't BE her during the race so don't even try. Also I recommend to begin with cave up above and also castle and you can just dodge witches instead of honestly defeating them all.
You can upgrade your boobs till maximum (8 or 9 I don't remember exactly) by finding milk in chest BUT after you collected all amulets you MUST deflate and expand through the statue or you won't enter to the final boss.
To defeat boss just spam her and dodge what you can but better just take all deflations. Game will over and you will restart anew, unfortunately no New Game + or anything. Assuming you didn't glitch any way up to this point ofc.