It came to my attention that there might be some bugs preventing you from finishing the game. Most of them can be fixed by simpling "Restarting" the level from the Pause Menu. Although, you might be unable to use the second stronger attack for the characters (Dodge roll, tackle and water bullets, respectively).
If you were stuck and don't want to replay it, you can watch a full playthrough I did of the game and posted on youtube here: