When the enemy reaches the player, the health should go down, but it says NaN(Not a Number).
The instance name of the Health text is Life, it's dynamic text and the variable is Health.
Health = 0
Life.text = "Health: " + Health;
_root.Health -= 1;
whatever variable you use to store the health of your player should NOT be a textfield variable.
Then what should it be?
a number variable.
in as2, you don't even need to declare it. just don't declare it as something else which is what you're doing when you used a textfield variable (which is always a string).