Janna is the evil god of death and destruction, and the main villain of Ghostbusters Sega game set between the two movies. She first appears to them in a human form very similar to that of Gozer, but than morphed into her true, monstrous appearance.
Janna sets out to open portal from her dark realm into New York. To do this, she uses pieces of ancient tablet capable of opening such portal as a way for her lieutenants to enter the city. She received help from Arthur, a man corrupted by her power. A massive ghost outbreak led by her lieutenants took place in the city. Earthquake, the first signal of her coming, also makes things worse.
As Ghostbusters started to collect these tablets and defeat her lieutenants, Janna manipulated them to collect them all and open the portal to her realm. In the end, the team enters her realm, defeats her and finds a way to close the portal, saving the city again.
Janna had four ghostly beings that served her as lieutenants. Each of them was summoned to New York by a piece of stone tablet. Ghostbusters defeated each of them, but very able to finally trap them only in Janna's domain. Also, Janna created the fifth lieutenant from the mind of a man who enjoyed Stay Puft Marshmallows, thus recreating the giant Stay Puft, who, however, was destroyed as soon as Ghostbusters confronted him. Janna's lieutenants are:
While not explained, the booklet for the video game notes a boss being Bazoozoo which could translate to Pazuzu which is king of the demons of the wind, and son of the god Hanbi. One could conclude that probably this is the name of the form of Janna.
Pazuzu is a Mesopotamian and Sumerian wind deity and the son of Hanbi or Hanpa, who is known as the god of demons, lord of all demons, and king of evil. Pazuzu is said to rage like a whirlwind bringing disease to mortals. He has four wings, a half-human and half-animal head, with a ram's horns, and his hind feet are talons. His body is covered with scales or feathers. He has the tail of a scorpion and his phallus terminates in a snake's head.
In Assyrian mythology, Bazuzu or Pazuzu is a demonic deity of the elements.
In all versions, he is known to have a wife named Lamashtu.
Janna is an Arabic term for the Islamic version of the Garden of Eden. Formally, it is called Jannatu el-Khuld, "Garden of Eternity" and is symbolized by green or yellow coral. It is considered the first stage of Islamic paradise.
Likewise, Islamic purgatory is called Jahannam. 
- Turner, Patricia (July 2001). Dictionary of Ancient Deities, p. 14, 243. Oxford Press, New York NY USA, ISBN 0195145045.