Robb13's Big Adventure

Robb13's Big Adventure looks nice but there are a few issues.

Suggestions for improvement:
1) There is a so called "grace period" in a lot of platformer games which allows the player to jump a short moment after leaving a platform.
This will make the game more "forgiving" and walking and jumping feels more fun if you do not have to be perfect whenever a gap appears.
2) Some coins are not collectible without falling into the abyss. Does not feel that great. I know because I collected them all.
3) The skeletons are not a threat. I think they are supposed be an enemy but they hit air and you are not punished for touching them.
They feel like funny little critters.
4) Is there a way to hit the boss without getting hurt? Your game does not have any kind of tutorial and the move set is not clearly communicated to the player.
5) Revise the current levels than add the same amount trying maybe some different challenges.