O wait, i forgot something, if you go back here this "hole"... well... is not a hole. I forgot to send this last time. 
And i guess this knife is not supposed to persist after killing the boss.
I know for sure this is not intended but it made so easy to dodge the annoying monster.
You can jump over a wall of one tile, horizontally.
And lastly, i really like the game so far, i'll be wating for next chapter.
pd: oh and sorry for my poor english, i'm not to good writing in english... i can read but when i'm writing i just put whatever comes to my mind without thinking too much about grammatical.