hmm,, Maths =D
-(x * x) makes a parabola from low to high, and to low again,
so it would be: 100 -1 * ( x * x)
100 is the highest of the bullet,,
i dont know how to make it go that way, but that is the formula
maybe:
---------------------
Event : Cast ability
Action: set x = -10
---------------
Event: every 0.1 sec of the game
set y = 100 + -1 * ( x * x )
if x is greater than or equal to 11
----- Do actions to stop the whole missile
move 'bullet' instantly to (point with polar offset ( position of bullet, 10 + x range, facing of bullet degrees)
change 'bullet' flying height to y height at 0
set x = x + 1
-------------------------------------------
I know this looks like quite a big mess,, but i hope it helped
EDIT: the range of the movement of the bullet has to be + 10 to make it not go BEHIND the shooter ( or whatever it is)
This number has to be the opposite of the starting number of x ( x = -10, then the range + 10,, x = -20 then the range + 20)
Please dont ask me to give you a new starting number for x if you change the maximum height, i dont know how to do that!