Hi. Perhaps you missed one hidden item that was behind a "damaged" brick tile, that looks slightly different than the rest. There are a few places like that which can be shot with your fireball.
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Hello ! Thanks for your reply, but I tried again today, checked every room and checked the map, killed all ennemies and nothing :/
I just noticed there was a room i didn't go yet, at the top north-west, but i don't know if this is a bug or if there is actually a room after beating the bird... There are killing feathers falling now, maybe there is something to do here but i really don't know what to do...
Sorry to bother you ! ^^'
Hello ! I didn't find it so i started a new game, and finally completed 100% !
I was stuck at 99% too, but this time when i went back, the teleporter which is activated by breaking a block in middle tower was disabled, so i broke it and it worked !
Thanks you for your help, a really nice game despite some bugs ahah ! ^^