Thank you for your comment and feedback! We've changed the squirrels and bats' HP in order to make the game less difficult. About having to shoot them 8 times, it's probably easier if you use the charged attacks.
Regarding the ending, our intention was having a boss battle, but we couldn't make it in time and had to change the story accordingly. :/
We're taking your first suggestion into consideration, while the second was something we decided to leave as it is. The gameplay isn't about using every power at once, but choosing which is going to be more helpful at the time. All of them have weaknesses and strengths, it wouldn't be challenging at all if there wasn't a downside to them.