नीलशिखण्डवाहनः

Source: TW

नील॑शिखण्ड॒ वा ह॑नः ।

The AV mantra nIlashikaNDavAhanaH is used in kaumAra parlance as the renowned aShTAkShari-vidyA. The word nIlashikhaNDa is a unique usage of the AV tradition that is not endogenous to the RV, YV or SV. It likely emerged as a term in the Indo-Iranian border zone where the core of AV tradition developed.

It is specifically applied to rudra or his ectypes bhava & sharva which some traditions see as his twin sons ~ ashvin-s of the RV. The AV usage likely parallels the nilagrIva of the YV tradition that became dominant in the later H tradition. AV-vulgate 6.93.1 refers to sharva rather than skanda (yes the 2 are related). The interpretation of AV-vul 20.132 in the vaidika sense goes thus:

द्वौ वा॒ ये शि॑शवः ||15||
The two are indeed auspiciousness & might; +++(पदे लुप्ते ऽत्र?)+++

नील॑शिखण्ड॒वाह॑नः ||16||
O blue-crested one! He is verily the killer.
+++(वा हनः इत्यत्र तु स्वरं दृ‌ष्ट्वा “ऽहनः” इति स्वीकर्तुम् उचितम् भाति - तस्मिन्नेव पक्षे स्वरनिघातो भवति। वाहन इति वा।)+++

Thus, the two auspiciousness = bhava; might= sharva; of them the blue crested one – likely sharva is a killer. Thus, the vaidika usage it was likely related bhava-sharvA which makes the kaumAra bahuvrIhI interpretation still compatible with old tradition.

These incantations are said to be the mysterious “prattle” of my ancient clansman aitasha: the aitasha pralApa whose magical meaning was misunderstood. In them, the reference to the golden camel is an element that links the AV tradition with the I-Ir border zone – it is notable that the founder of the Iranian counter-religion was also known by the name of the golden camel.

But the Kyanokhaitis parallel in the Orphic incantation is also striking as you note. They might have some deep albeit tenuous link: the sea-> Kyanokhaitis; the churning of the sea -> nIlagrIva; was nIlashikhaNDa also related to the marine allusion hence?