You've unlocked the wall kick.
After you jump, move towards the wall and when you get close to the wall, jump again!
Was there extra content after you defeat the boss? I saw screenshots there was an additional enemy that you would fight after fighting the final boss (EDIT: I Found it) NEW QUESTION: Where do I find the Shake to give to the Snake in the factory?
Please investigate the area where boxes fall into the large hole in front of the boss room.
There are shiny items there, so please pick them up.
Only problem (look to the left)
Only problem (look to the left)