This is following my rather speculative ideas about the sammapasa:
Niraggaḷa means “unbarred, unrestricted”. The Buddha used it as an epithet of a mendicant who has become free from the five lower fetters (AN 5.71:6.1, AN 5.72:5.1, MN 22:34.1). He adopted it from the brahmins, where it was the name of a sacrifice. However it is not a regular or well-defined name, so the exact sense is uncertain.
In “Additions to the Study of the Niraggaḷa, etc.” (Annals of the Bhandarkar Oriental Research Institute LIII, nos. 1–4. (1972): 195–199) Thite shows that niraggaḷa is used in a few different ways.
One passage of the Mahābhārata describes it as a sacrifice of the sap of all trees, and Thite regards this as the original meaning.
But a prominent sense is the form of horse sacrifice when the horse wanders without restriction for a year, otherwise known as the “universal sacrifice” (sarvamedha). This sense is given in the Pali commentaries as well as the Mahābhārata and Vāyupurāṇa. It seems likely this is the meaning in the Pali texts.
If these identifications are correct, then all five of the rituals mentioned in the Brahmanadhammikasutta (Snp 2.7) were cruel rites that demanded the slaughter of men or beasts in order to establish royal authority over territory. As a reward for the religious sanctification of temporal authority, the presiding brahmin priests would receive a handsome reward (dakkhina).
Edit: never mind I just found it- according to the Padma Purana, an elephant is killed at the Pundarika sacrifice referenced in Mvastu, and also at an “elephant sacrifice” (the Paduma sacrifice?)
So the Chinese seems to reference Pundarika/Paduma(?)/“elephant”, Asva and Nirargada. It’s interesting that this unique pairing occurs across both MA and the Snp parallel.
Given that the pundarika sacrifice is referenced in a Gupta inscription, it might have been more contemporary for the transmitters of the Chinese texts.
Oh, interesting, you also have the thing where an elephant is called “padumi”, for which a variety of explanations has been offered. But surely the obvious reason is that they love to hang in lotus ponds to bathe and eat?
