In the beginning of the fourth season of Sailor Moon, entitled Sailor Moon SuperS, Chibi-Usa/Rini takes center stage in the story when she has a dream about a mysterious winged unicorn calling itself Pegasus. The Pegasus speaks to her with a human voice, but tells her not to tell anyone about the dream. Chibi-Usa carefully guards the secret, even when it is later revealed that there is a new team of bad guys and that Pegasus plans to give Usagi and Chibi-Usa new powers (since it is a new season, after all!). Of course with new powers come new bad guys, the Amazon Trio, representatives of a crazy circus from outer space who are trying to find and capture Pegasus, by looking for girls who have beautiful dreams.
SuperS, like most of the series, was better in the manga. The English dub also makes the original worse/dumber in my opinion by emphasizing the comedy of the show even though this arc is more serious in tone than the first season.
This series focuses more on Chibi-Usa, whereas the previous seasons focused on Usagi. This can be a good thing or a bad thing. On one hand, it is good to change up the feel of the show a bit (even though it retains the cliche formula of the rest of the show). On the other hand, it's a little bit creepy having Pegasus appear to Chibi-Usa in a dream exclusively and not to both her and Usagi, and it's more than a bit creepy that he tells her not to tell ANYONE about the dream. He could have said, you can tell other Sailor Scouts, at least? And if you don't really like Chibi-Usa as a character, while this story arc may redeem her for you, having the story revolve around her as the new Chosen One isn't going to sit well with you.
Another problem with this season in particular, is that the villains are not really scary, and the Monster of the Week/ Girl in Distress of the Week formula is still just as grating as it was in previous seasons. At least in the first season, Queen Beryl and Queen Metalia were scary, but in this season, the bad guys are all doofy-looking circus freaks. They show up, they look into a girl's dream to see if Pegasus is there, and then they leave. This doesn't really seem to have the stakes as high as the confrontations with Beryl, Black Lady, and Kaorinite. The girls get a really cool power boost, including the ability to summon Pegasus who gives them more power, but it just feels like that awesome new boost is being wasted on such pissant villains.
Not my favorite arc of the whole series, but I definitely found some things to like about it. I liked Pegasus, and I liked seeing Chibi-Usa get more used to being a Sailor Scout in her own right (even though I saw her as a weird intrusion into the show in the first place, this arc helps her kind of grow on you a little bit). It still had all the good and bad things that were in the first season, but luckily, by now there is less drama and petty bickering between main characters, making the group more functional, which was kind of nice. But it's still very much the Sailor Moon status quo too.