Pegasus is a magical creature with the ability to communicate telepathically. This is the form that Helios’ spirit takes while he is on Earth, and he is hiding in Chibiusa’s beautiful dream since he cannot survive on Earth otherwise. Pegasus is a MUCH more powerful being in the anime than he is in the manga; he gives Sailor Moon and Chibi-Moon new brooches which permanently upgrade them to “Super” form, and later gives the Inner Senshi “Super” upgrades of their own. He gives Chibi-Moon the “Crystal Carillon,” which can summon his power whenever needed. After being called, he charges up Sailor Moon’s Kaleidomoonscope to perform “Moon Gorgeous Meditation.” (Chibi-Moon has the ability to use “Moon Gorgeous Meditation” in the manga as well.) Since baby Hotaru performs the same Super upgrade later on in Stars, it’s possible that anime Pegasus has power equal to Saturn’s.
In the manga, Pegasus sees a vision of the future of a maiden approaching him, and he believes she has a beautiful dream powerful enough to break the seal on the Golden Crystal. He initially mistook this vision to be of Usagi, but it turned out to be Princess Lady Serenity, Chibiusa’s future teenage form. It is revealed halfway through the SuperS anime that the bearer of Pegasus has a golden Dream Mirror (which is implied to have gained that colour because of the Golden Crystal). The beautiful dream that Pegasus hides in is eventually revealed to be Chibiusa’s desire to be an elegant, curvaceous and mature woman like her mother. (Meaning Neo-Queen Serenity, not Usagi.) When Palla-Palla switches Chibi-Moon and Sailor Moon’s ages, Chibiusa could not connect to Pegasus anymore, because her dream was “granted” by the power of the new moon, and it obscured her real dream.
Pegasus is a famous creature from Greek mythology. It is usually depicted as a white horse with wings and the ability to fly. What makes Sailor Moon’s Pegasus different is that he also has a unicorn horn, which in the anime is revealed to be the Golden Crystal in disguise. It is eventually revealed that Pegasus’ true form is…
Helios, whose name comes from the Greek mythological God of the Sun (hence why he is unofficially considered to be Sailor Sun), is a Priest of Elysian, a magical kingdom hidden deep within the Earth. “Elios” is an alternate phonetic spelling of his name. Helios has guarded Elysian, Endymion’s kingdom, since the era of the Silver Millennium. He has the appearance of a thin, white-haired young man in his early teens. He also held guardianship of the Golden Crystal, which Queen Nehelenia coveted. However, she did not have a beautiful dream, so she was unable to use its power. Instead, she trapped Helios in a cage within her world of mirrors, and only his spirit was able to escape and take refuge in Chibiusa’s dreams.
It is strongly implied that in the future, he and Chibiusa will reunite and he will be Chibiusa/Princess Lady Serenity’s lover. His relationship with Chibiusa is gradually built up to be a romantic one; in the anime they talk secretly together and he gives her advice about friendship and love, and is barely able to conceal his own feelings for her. She utterly trusts him, despite his being secretive and refusing to answer many of her questions. In both the anime and the manga, he is Chibiusa’s first kiss.
As this is another concept from Greek mythology, there are variations on how to spell Helios’ home. I use “Elysian,” but you could spell it as Elysion, Elysium, etc. It is also sometimes referred to as the “Elysian Fields.” In Greek mythology, the Elysian Fields were a place in the afterlife; one of the levels of Hades. It was somewhat similar to the Judeo-Christian concepts of Heaven, in that the righteous and brave spirits of the departed resided there. In the series, it is depicted as a once beautiful and magical place ravaged by the destruction of the Dead Moon. It is implied that the place where Chibiusa meets Pegasus in her dreams is how Elysian is supposed to look.
Elysian was the true home of Prince Endymion’s court, and it, Helios, Endymion and the Golden Crystal are connected in spirit. Helios’ duty is to protect Elysian and Prince Endymion by praying for them. So when the Dead Moon begins to attack Elysian, Mamoru fell gravely ill. In the manga, the illness is described as a shadow on his lung. Helios revealed that the shadow is a black rose growing within him and Mamoru. He warned the Senshi that if the Dead Moon are not stopped, both he and Mamoru would die. In the anime, Mamoru collapses with illness when the Earth itself is attacked (with the entirety of Tokyo being covered in cobwebs).
THE GOLDEN CRYSTAL
This object has two VERY different origins/uses in the anime and manga. In the anime, the Golden Crystal took the form of Pegasus’ golden horn, which was why he was powerful enough to grant all of those upgrades. The Golden Crystal was the only way to defeat the Dead Moon, as for plot reasons, the Silver Crystal was ineffective. The Dead Moon was made up of the wasted dreams of Queen Nehelenia’s court. They had forgotten how to dream because Nehelenia consumed their Dream Mirrors to keep herself young. In the anime, Sailor Moon and Chibi-Moon both used the Golden Crystal to combine their powers with people who have beautiful dreams (we see former Victims of the Day praying alongside the Senshi). This sealed Nehelenia in the New Moon, and Helios took the Golden Crystal back to Elysian.
In the manga, the Golden Crystal belongs to Mamoru, and is equal to Sailor Moon’s Silver Crystal. It is also his Sailor Crystal, and designates him as the representative of Earth, so he’s the male equivalent of a Sailor Earth. The Golden Crystal had been sealed within Mamoru’s body. When the Silver Crystal evolved to be the Silver Moon Crystal, this broke the seal. The combination of the two Crystals and the Senshi’s powers sealed Nehelenia within her mirror once more. Usagi and Mamoru then took the forms of Neo-Queen Serenity and King Endymion, and Helios affixed the Golden Crystal to the top of Endymion’s cane. In the anime, Mamoru never takes possession of the Golden Crystal. It is revealed in Stars that his Star Seed is gold-coloured, but it is a different object than the Golden Crystal (rather than them being the same object in the manga).
When it comes to the Golden Crystal, there is one unanswered question. We know that as the daughter of Sailor Moon, Chibiusa is able to use the Silver Crystal. But could she also use the Golden Crystal? Although she is also the heir to the Earth Kingdom, Chibiusa’s Earth powers are never explored. One might presume that the powers of the Moon eclipse (pun intended) those of the Earth’s. Rather than using the same Sailor Crystal as her mother, however, Chibiusa gains her own unique Sailor Crystal, the Pink Moon Crystal.
Manga panel scanned by Miss Dream and coloured by me.