Add a sprite to use as a line, and make it's origin centered on the left. Also make it's height 4 or something, that will be the line thickness. Name the sprite "line".
Then you can use the qarp() expression to do the curve and you could do this:
global number px=0
global number py=0
every tick
--- line: destroy
--- set px to start.x
--- set py to start.y
repeat 100 times
--- create line at (qarp(start.x, (start.x+end.x)/2, end.x, (loopindex+1)/100), qarp(start.y, (start.y+end.y)/2+200, end.y, (loopindex+1)/100)
--- line: set angle toward (px,py)
--- line: set width to distance(self.x,self.y,px,py)
--- set px to line.x
--- set py to line.y
it's fantasy! but , it's also executing each tick and such more objects were created ...