"Crazy Ex-Girlfriend" did a thing that used to be more common. They brought back a character with a different actor. Obviously, as adults we know that people have to take jobs and opportunities on the table, and if your show would like you back in a future season, but you book, say a Broadway show, well, we all get it. But of course, just as a show makes side notes about the new guy this season, season meaning the quarterly one because of course anything else would be a weird way to talk about you life, they weren't going to do it and not talk about it.
It was time for a high school reunion. And of course that meant Josh had assigned extra importance to his role as prom king. And it meant Rebecca pondered - as her friends all made big life changes, if maybe she had overanalyzed and missed out on a true love. Heather and Valencia both said of course it was Greg, which seemed, maybe not entirely in keeping with Heather and Valencia. Rebecca said well, except for how they were toxic and brought out the worst in each other, so basically only if he was like an entirely different person. And then an entirely different person walked through the door.
It is a credit to many things, casting, writing, and the acting skills of Skylar Astin that by the end of the season (and by this I mean TV season) I had to keep reminding myself that Santino Fontana originated this role. It isn't that I will ever forget "Settle For Me" or let's get drunk and make fun of people, because I will not. But the show made me believe that sober, getting his life back together Greg looked like Skylar Astin.