To draft the pattern of this slip dress, start from a basic block with darts.
Mirror back and front for the asymmetrical style.
Draw the neckline and widen the shoulder dart by 1cm, reshape the waist dart to make the underbust fitted.
On the skirt of both back and front draw the curved hem, reshape the side seam and draw the slash lines for the drape.
Trace the front and back as you see here.
Cut through the back lines and close the darts.
Open the drape and redraw the whole piece marking the pleats.
Do the same on the front closing the shoulder darts and opening their volume at the bottom of the dress, redraw the whole piece with the neckline part mirrored upwards.