Vishwaroopa Dharshan means showing (or) exposing his original representation in a very big way. Sriman Narayanan has shown his Vishwaroopa Dharshan in various aspects of time to various people. As soon as we think of Vishwaroopa Dharshan, next second we will think of the great Dharshan of Sri Krishnar shown to Arjunan during the Mahabharatha war. Let us now know about this Vishwaroopa Dharshan shown by Sriman Narayanan and also some of the other Dharshans towards various persons.
The Great, Vishnu Puranam says that Sriman Narayanan is surrounding this entire world like water, air etc. What we see in this world is the reflection of Sri Vishnu. During the Avathaar of Narasimham, Sriman Narayanan shows his Dharshan as "Sri Narasimhar" to one of his great bhaktan, Prahaladhan. He gives his seva along with Sangu and Chakkaram.
Yet another great puranam, the Bhaghavatha puranam explains the greatness of Sri Krishnar as how he gave his Dharshan towards Gajendran, the elephant. Gajendran elephant used to dedicate a flower towards the divine feet of Sriman Narayanan and it did this activity as a daily practice. Likewise, one day a crocodile caught its leg in the pond where it used to pick the flower for Sri Vishnu. Gajendran raised its voice towards Sriman Narayanan as "Aadhi Moolamey" and seeked for help. As a flash, Sriman Narayanan in his Garuda Vahanam came there and killed the crocodile using his Chakkaram and helped the Gajendran. And finally he was blessed by Sriman Narayanan and got the Moksham (Heaven) and this activity is greatly explained as "Gajendra Moksham". This action of Sri Vishnu clearly explains that his graceful hands will be extended not only for the humans but also for animals too.
During the time of Krishnavathar, Sri Krishnar showed his roopams and Dharshan to Various peoples. When he was born in the Prison, he showed is original roopam (as Sri Krishnar) who exactly he is to Vasudevar and Devaki. And in the time of Gurukshetra (Mahabharatha) war, he showed his roopam to all the Panja Pandavas.
After Karnan was killed by Arjunan, and as requested by Karnan, Sri Krishnar showed his Vishwaroopa Dharshan to him.
As explained in Bhagawad Gita, Sri Krishnar explained the Geethai and about Karma. During that time, Sri Krishnar showed his Vishwaroopa Dharshan to Arjuna and blessed him with his grace to win in the war.
So, let us also dedicate our prayers and Bhakti towards Sriman Narayanan and get his grace to attain Salvation (or) Mukthi.