The Tamil village guardian on horseback was absorbed over the medieval centuries into Shasta, the son of Shiva and Mohini, and the Sanskritising continues today.
South India · Tamil NaduFolkTamil village communities
Ride out of any Tamil town and the first shrine at the field's edge is usually Aiyanar's: a moustached rider with a sword, a row of terracotta horses at his feet, and the darker guardians Karuppasamy and Madurai Veeran beside him. He is a boundary god, patrolling by night and answering for the village's safety. Henry Whitehead described these shrines a century ago, and the pattern still holds. What has changed is his family: from the medieval period the guardian was matched with the Brahmanical Shasta, the son born when Shiva met Vishnu in his Mohini form, and the process has not stopped. Reporters in Tamil Nadu now find village priests trained to dress Aiyanar in Puranic ornaments and recite Sanskrit for him.
In the Puranic account Shasta or Hariharaputra is the child of Shiva and Mohini, the enchantress form Vishnu took during the churning of the ocean; he is a divine son of two of the three gods, with no village boundary to guard.
What is different here:
The Puranic Shasta is a cosmic son of Hari and Hara; the Tamil Aiyanar is a local rider who guards a specific village and was matched to Shasta only later. The horse, the terracotta offerings and the attendant guardians belong to the village layer.
Sources: Aiyanar — Wikipedia; Village deities of South India — Wikipedia; The Village Gods of South India; Sanskritisation of Tamil Nadu's village gods; Village gods of Alanganallur, Madurai; Sastha (Aiyanar)