Birth of Grass

The Nagalingam installed by King Dasaratha is preserved in this temple for getting Four Children.

The place Temple is also hailed as

1. Pullaranyam, 
2. Pullanai, 
3. Thiruvanai, 
4. Pullangadu. - Rama lay in meditation for three days (thiru)on the bed of grass(pull) and hence the name Thiru-pull-ani (Explains the Meaning of 1 to 4)
5. Dakshina Jagannathan as a salagram installed by Devas during the swayambu manvantharam. 
6. Adhi(Neel) Sethu, 
7. Nala Sethu, 
8. Rathnaakara Kshetram,
9. Dharbasayanam,
10. Saranagati Kshetram (Explained the Meaning of 6 to 10) 

Here, Vibishana makes his ‘saranagati’ (surrender) to Lord Rama. On his counseling, Lord Rama reposing on the dharba grass for three days, requests the Samudra Raja (Emperor of the Oceans) to give way to Him to go to Lanka. The Samudra Raja(Rathnaakara ) does not concede to His request and infuriates Him. The furious Rama takes His bow and warns the Samudra Raja that He would dry up the entire waters. The frightened Samudra Raja with his wives rush to him and surrenders and requests him to use nal neel to built a sethu here.

1. Because of surrenders by Vibishana and Mahodadi, the place is called ‘saranagati kshetram’
2. Since the Lord reposes on the darba grass, He is named ‘Darbasayana Ramar’.

This is the place where the messengers of Ravana, Sugan and Savanan met the Lord.

Thirupullani has the special distinction of having visited by Rama twice - before going to and when returning from Lanka.

1. It was here that he is believed to have reclined in meditation for three days, invoking Varuna.
2. When returning from Lanka, Rama after installing the Rama-linga at Rameshwaram, visited this shrine once again, the 'adi sethu', and it is here he is said to have had his holy dip to rid himself of the 'brahma-hatya-dhosha' of killing Ravana. 

72 Chatur Yugas ago, three maharshis,

1. Pullavar, 
2. Kannuvar, and 
3. Kaalavar

performed severe penance on Lord Mahavishnu sitting on the Darba grass. The Lord gave darshan to the Rishis in the form of an Pipal (Aswatha) near the shrine. Though they were happy to have the darshan of the Lord in the form of Arasu Tree they begged him to show them His original form. The Lord obliged and appeared as Adhi Jagannatha Perumal.

http://www.youtube.com/results?search_query=SriAdiJagannathaPerumal 

Puranas ascribe different reasons for the wild growth of Kusa grass in this particular spot.

Birth of Kusa - Dharba Grass

Lord Vishnu assumed the form of the 'Divya kUrma' tortoise which form Lord Vishnu assumed to hold the Manthara mountain that was used as churner in place, on His hard, rock-like shell. When the mountain was turned over and over again on His back in the efforts to churn the Ocean of Milk several hundreds of strands of hair on the shell of the Divya kUrma fell off due to the friction and were washed ashore and with the passage of time, they turned into Kusa grass. In fact, it is considered as a part of Vishnu himself. .

Addition of Nectar

The story goes on. When nectar was churned out of the ocean, Lord Vishnu assumed the form of a damsel, Mohini, and distributed it among the celestials. Several drops of nectar fell on the ground when it was distributed and also when it was consumed by the Devas. Such drops fell on the 'dharbai' or Kusa grass and therefore the grass is considered sacred as offering s of them to kusa grass .

Diety

On the outer mandapam of the ‘Darbasayan Ramar’ shrine is a small shrine dedicated to Santhana Gopalan, known as ‘Nagar Mandapam Santhana Krishna Mandapam’. It is a lovely sculptural wonder. Lord Krishna (Mohini)sits on the Adisesha who rests on the ‘kurmam’ (tortoise) surrounded by eight elephants and eight serpents.

There is a Santhana Gopalaswamy Sannidhi, where King Dasaratha with his three wives was prayed to Lord Krishna for an offspring.

Thatho Yagjey Samapthey Thu Rithunam Shat Samathyayu:
Thathascha Dhwadhashey Masey Chaithrey Navamikey Thithou
Nakshathreydhithi Dhaivathye Swocha Samstheyshu Panchasu
Graheshu Karkadey Lagney Vakpathavindhuna Saha
Prodhyamaney Jagannatham Sarva Loka Namaskrutham
Kousalya Janayadhramam Divya Lakshana Samyutham
Vishnorardham Mahabhagam Putram Ikshuvaku Nandanam.

(Srimad Ramayanam – Bala Skandham)

Festival

The eighth day of moon in the month of Badra (September) is observed as Darbha Ashtami and is an annual festival in this shrine.

108 Sangu and Kalasa Thirumanjanam
http://anudinam.org/2013/07/19/108-sangu-and-kalasa-thirumanjam-for-adhi-jagannatha-perumal-at-thirupullani/ 

Sea Deities

Another landmark and a small temple is ‘Chinnakoil’ (small temple) situated about 3 furlongs from the seashore. It houses Lord Srinivasa and has beautiful sculptures. On the northern side there is the white-image of ‘Swetha Madhavan’, found from the sea. This is a marvelous sculptural piece, lauded by the Archeological Survey of India. Another interesting image is that of ‘Agasthyar’, found from the sea. There are water-eroded marks on the knees of the image.