I just found the answer to my question, according to the SRD there is a type of unicorn called a celestial charger that is a Celestial Unicorn. In 4e I believe the celestial charger was just a celestial horse, but maybe I'm wrong. I remember the Unicorni 4e being a fey being. Of course in 4e elves and gnomes where fey too, and now its just a linger ancestory in elves and nothing in gnomes.
Still its a legendary creature, so when a Cleric or Bard who uses his magical secrets to gain the spell summons it, it should be able to use legendary actions right?
Still its a legendary creature, so when a Cleric or Bard who uses his magical secrets to gain the spell summons it, it should be able to use legendary actions right?