Shiva Incarnation as Mahesh and Vrishab

SHIVA'S INCARNATION AS MAHESH
Once, Bhairav who was entrusted with the job of a doorkeeper became so infatuated with Parvati's beauty that he tried to prevent her from going outside.
Parvati became furious and cursed him to be born as a mortal man on the earth. Bhairav became very sad but now the damage had been already done. Bhairav later on appeared in the form of a man named 'Vetal'.
Vetal prayed to lord Shiva who took his incarnation as Mahesh and goddess Parvati as Girija.

LORD VISHNU CREATES TURBULENCES

After the churning of the ocean had been accomplished, numerous things had emerged out from the ocean. Jewels, Moon, Lakshmi, Poison, Uchchaishrava horse, Airavat elephant, Vessel containing Nectar were some of the things which emerged out from the ocean after the churning.
A tremendous battle was fought between the deities and the demons to have control over the vessel containing Nectar. The demons had snatched that vessel from the deities.
By the divine inspiration of lord Shiva, Vishnu appeared in the form of Mohini the enchanting beauty. He successfully recovered that vessel from the control of the demons.
To distract the attention of the demons from the nectar, lord Vishnu created numerous enchanting beauties. When the demons saw them, they forcibly carried these enchanting beauties to their abode, the Nether world. After that they again returned to take control of the Nectar.
By that time, Vishnu had made the deities drink all the nectar. When the demons came to know about this, they became very furious and attacked the deities. A tremendous battle ensured between both the sides. Ultimately the demons got defeated. To save their lives the demon ran towards their abode. Lord Vishnu chased the demons and entered the Netherland. He killed all the demons.
Lord Vishnu then saw those enchanting beauties who had been abducted by the demons.
Women who where created by Lord Vishnu , were fascinated by Lord Vishnu and did a huge penance to Lord Vishnu to have him as their Husband.Then as its duty of the god to fullfil wish and grant boon to his worshippers.
He Granted to the requested boon of having him as a husband by forgetting everything about his responsibility towards the world and started living with them leaving all his duties aside.

SHIVA'S INCARNATION AS VRISHABH
During his stay in the Netherland, many sons were born to Lord Vishnu, who were very wicked and cruel. These sons of lord Vishnu started tormenting the inhabitants of all the three world. All the deities and the sages went to lord Shiva to take his help. They requested him to kill the cruel sons of Vishnu and reestablish him (lord Vishnu) in his own abode, which he had abandoned for the Nether world.
Lord Shiva went to the Netherworld in the form of an Ox (Vrishabh). He killed all the sons of lord Vishnu with his sharp horns. Seeing the death of his sons, lord Vishnu came forward to fight him. He attacked lord Shiva with his various weapons, but lord Shiva remained harmless.As Both the gods are equally strong and they are both non other the same as Shankar Narayan form both where fighting and that fight was never ending and no one is harmed.After many years of fight , Women who made Lord Vishnu forget everything due to the boon made Lord vishnu free from the boon, Ultimately lord Vishnu was able to recognise him.He eulogized lord Shiva.
Lord Shiva then requested him to return back to Vishnuloka, he accepted. Lord Vishnu left his 'Sudarshan chakra' in the Netherworld and went to his own abode, where Lord Shiva presented him a new Sudarshan chakra.