Nathan Forester decided to help out Derek Hale and also help out his new online friend...his online friend loved Robin Williams a whole lot and missed him and he sympathized with him...a long while ago he made a wish to Make A Wish but he didn't get to meet Robin since he basically wasted his wishes on a guitar, however Nathan decided to help that friend out by also granting a special wish that Derek had for Ryder's birthday and also granting the wish of the friend he cared about, that friend's wish was to meet Robin Williams but unfortunately Robin's passing got in the way of that, luckily Nathan used his powers to transfer Robin's spirit into Derek's body, transforming Derek into Robin himself.