The Moroi Crystals are mystical ruby crystals created by the Vampire race in the realm of Vaeternus with the power to traverse between dimensions at will. They first appeared in Mortal Kombat: Deadly Alliance.
These legendary magic cystals that no one knew existed, can one to travel between the realms at any time. But the crystals can only be activated with a certain incantation in order to begin interdimensional travel. And only the ancient race known as the Moroi have that knowledge.
Long ago, the Vampires, especially the long-forgotten Moroi Empire, forged their crystals from precious stones within Veaternus, and used their sorcery to fill the gems with condensed magical energies permanently, thus each individual vampire use their ability through these gems to travel to other realms outside their home.
The Moroi Crystals were put to good use once again after the ruthless Emperor Shao Kahn conquered and merged Veaternus with Outworld. The Vampires who have complete disgust and hatred towards the warlord who invading and ruined their once glorious home, use their crystals to escape to other realms, new ones they have found and entered, and old ones including Earthrealm they've already explored.Centuries later, the vampiress Nitara while bearing a Moroi Crystal attached to her necklace, finally obtained an orb to free her old homeworld from Outworld with the aid of cyborg ninja Cyrax within an undergound incubation chamber. She then took her necklace and uttered a mystical incantation to open a swirling portal around him, just as he only had time for a solemn bow before being swept into the vortex. Nitara actually fulfilled her end of the bargain when she sent Cyrax back to Earthrealm, and she was finally all alone as she destroys the orb and freed her long-lost homeworld.