Nice game !
I personally think putting all the text in the door level that has a timer is not a great idea, if you want people to read the controls dont put a timer of 10 seconds to beat the level (altough you just lose 1 life and you are full life in the next level, the player doesnt know it). I chose the door level 3 times in a row in order to read all the text. I suggest entering door level (with no timer), showing only the first 2 lines of the text and putting press space to continue, then 2 lines more of text and space to continue, another time (shows all the text) and then press space to begin and tjhe timer starts and you can play. (next time you choose the door level this tutorial wont appear, it will appear as it is currently on the game) Another thing is that blade is "impossible" to beat, my best battle left him with 7 hp, but the game is about finding 1s and searching if they have a 2 next to it, then a 3 etc, that is difficult cause in most cases in the whole screen there are like 8 ones, but only three o them have a 2 next to it, and if blades change them you cant do damage in the whole level. I suggest making maps so you can start with bigger numbers (now its always 21 or 321, i almost did a 54321 but a blade changed it) and i would made blades appear less often so the game feels possible to win.
The art is nice, the music is nice, its a short fun experience, i hope you continue developing it and polish so its not that hard.
Also, you can try my game if you want, it just takes 5 minutes ;)