who was the ghost?

There was no ghost. It was an old, retarded Freddy living in basement with Shiv's mother.

Vyom was not dead. He was using skin grafting to stay young and pretending to be Akash. Mrs. and Mr. Bedi had asked Odhni's help in locating the next incarnation of Sharanaya, but she switched the baby with another one. Mrs. and Mr. Bedi raised Shivani assuming it is Sharanaya, but actually Radhika was Sharanaya, Krish's (Shiv) secretary.

After lots of twists and turns, Vyom killed Shivani after knowing the truth. Mrs. and Mr. Bedi realized that they have created a monster. Vyom locked them in basement as well. Radhika remembered her punar janam and sent Krish waay to protect him telling him that she loves Vyom, but he got to know that Akash is 52 years old and came back to tell the truth to Radhika. Vyom stabbed him in the back in old style, and then took everyone to Mandir on gunpoint (Looked like a portable version of Kapali Hills Mandir)

Vyom was about to put Sindoor on Sharanaya when Krish arrived there (An alive Krish, for some reason, is way stronger than Shiv's ghost. Vyom went into SRK's Dar mode). Krish threw away the sindoor plate resulting in sindoor falling over Radhika. Vyom told Radhika that Sharanaya has to kill Shiv or he would keep reincarnating and forced her on gunpoint to do so, else he would kill his parents and Shiv's mother.

In the end, Krish kiled Freddy and beat Vyom black and blue. Krish and Radhika married while Vyom watched like an injured tiger. He jumped from the cliff saying "Vyom ki dewangee etc etc."

Krish and Radhika were in their bedroom having their Suhaag Raat while a strong wind started to blow, candles flickered and mirror shattered. Vyom, in black dress with black eyes, appeared in the broken pieces of mirror.