But dungeon 2 cannot be finished before visiting dungeon 4 because you need the flippers to reach the boss room.
Ok, I assumed that the dungeons should be completed in order because they are numbered. But maybe I've also misunderstood something due to my limited french knowledge.
The second dungeon boss is so easy with the second sword x)
Oh yes

I was like "oh no, I'm gonna die! wait, why is the boss nearly dead now?"
Two new things:
1.) The shift-running command sometimes works when swimming and sometimes doesn't. Which one was intended?
2.) I don't know how, but I managed to screw the controls up a little bit. Because somehow caps lock is now normal speed and disabling caps lock makes the hero faster.
EDIT: I just found out that this happens when changing the caps lock outside of the game. So if I minimize the game, enable caps lock and open it again, the hero still walks with normal speed.