How I understand, 4th area spawns when you enter a rest room and room-clear-count is 45+. Using SaveCrystal halves rooms-cleared-count.
here should be couple of edited savefiles , in one of them save is in 4th Lily Cave
1. BOSSRUN - my personal quick run through the game, I think I edited myself an OP staff at the start.
2. PLUS - all Shortcuts, all magic flowers except Peach and Lily equipped, different hacked OP staffs in inventory
3. PlusCave - same as PLUS, but savespot edited to the bottom of Lily Cave
hope I didnt mess up
From the bottom of Lily Cave, there are exits to the right to continue exploring, top-left for the room with lot of animation, down-left for the secret boss, talk to Octopirate mid-right to leave
Saves for me on Windows 7 are in C:\Users\~CurrentUser~\AppData\Local\flowerwitch
data.bin
Edit: also adding data.rar - save PlusCave, but with most Items unlocked (except 94th, adding which might keep secret boss from spawning) and a number of Bed items - go home to your bed and there should be an option to use those