Hylics: All Bosses and ending

I've Beaten this game twice now and I still have no clue what the heck is going on. There's only 4 required bosses but the video also includes the 3 optional bosses I could find.
0:00 Horrid Projection
2:48 Mustelidae (Optional)
4:30 The Creature (Optional)
8:23 Dark Knight Pongorma
12:31 Tomb Shrub (Technically optional)
16:18 Clawman
19:55 Lord Gibby
for those wondering if your movements are just right you can run around tomb shrub and skip the boss fight (big for speedruns) and the Clawman will ask for the password but he's just screwing with you so you since to my knowledge there isn't a password.
What a weird game