The forth season introduces a lot of new characters. Introduced are Pegasus/Helios, The Dead Moon Circus lead by Queen Neherenia and direct flunkie Zirconia and consisting of the Amazon Trio and The Amazoness Quartet.
The Amazon Trio is made up of Fish Eye, Tiger Eye and Hawk Eye. The Amazoness Quartet is made up of CereCere, JunJun, ParaPara (pronounced PallaPalla), BesuBesu (pronounced: VesVes). The Dead Moon Cirus is seeking the golden crystal in the horn of the Pegasus.
To find it they have to find the the person with the golden dream mirror. Pegasus is hiding in the beautiful dream of whomever has that mirror. (Every one has a dream mirror that allows people to see a person's dream.) The Pegasus gives Sailor Moon and Sailor Chibi-Moon new powers and items. The scouts want to save Pegasus and protect the dreams of the people of Earth from the Dead Moon Circus and Nerhernia. Nerhernia wants to use the golden crystal to rule the Earth and stay beautiful forever. She also tries to steal Darien/Mamoru away from Sailor Moon.