Lets start with getting the position of the mouse cursor:
Next we need to see how we draw.
And to bring it all together we take a look here:
Basicaly you get the start point from where the arms should spawn (Your character i assume). And the end point of the arms, which is your mouse cursor. Inbetween these points i would find the middle point (like (target.position - start.position) / 2). Between the start and middle point create a curve, and between middle and target point create a curve. The curves should have opposite curving.
Finnaly in your _process() function you start drawing some part of the curve till you hit the target.
