With one of the new characters introduced in the movie, I’ve seen people talking about Catrina so I decided to draw her.
 
I believe Catrina taught Star Swirl magic after he helped her get rid of her witch weed problem. This is why he was so good at magic as his professor is from a species that existed before ponies and knew many magical secrets.
 
Below is how I think Catrina and Rep would look like in current times. Catrina is still alive because she eat a magical herb that extendes her life (but don’t stop her from aging) and Rep, like a dragon, can sleep for long period of time to save his strength and live longer.