What's wrong with my code?

[Mr Wabbit]

1> If you are getting 1010 you var is set wrong.
You will have

var exp = "10";

You want

var exp = 10;

The "" means it processes the var as a string so you are asking it to add 10 to the string ie 10+10=1010, without the "" it becomes a math problem 10+10=20

2> Your Actions Frame want to be at the highest level and spam the few length ie
My example shows the timeline

_root level
actions - F1 -> F10
Movieclip - F3 -> F4

Our Root level spans 10 frames in this instance, the actions covers all 10. You want to cover all your frames with the action line.
If you go to a frame without the var on it, when it next goes to a frame with it, will reset.

3> Try to avoid buttons, you want your code at the highest level possible to avoid issues, and make decoding easier.
You can use a movieclip as a button, and the following code on the _root timeline actions.

myButton.onPress = function(){
	gotoAndPlay("styxgood1");
	exp += 10;
        mymc.Styxexp += 10 ;
}

Out of interest why do you have 2 exp vars in 2 different places?

This is a image from one of my project to show you what I mean by the actions covering all.
fk1x.png