There was a query regarding the correct form of mantrarAja.
The shrIkula tantras, when describing the gurumaNDalam, speak of the saptaviMshati rahasyas, elaborated through the shloka: shrInAthAdi gurutrayam. There is a mention of mantrarAja here. There are two opinions as to what this mantrarAja really is. There is a short mantra seen in AmnAya ratnAkara, AmnAyasAra, saubhAgyalakShmI kalpa, chinmAtramAlinI etc. which is also recorded by brahmashrI chidAnandanAtha in his saparyA paddhati. The same mantra can also be seen in shrIvidyA ratnAkara of H H karapAtri svAmin (on account of this work being a reproduction of chidAnandanAtha’s saparyA paddhati). If I remember correctly, it is this mantra that is also recorded in the AmnAya collection of H H Svamiji Maharaj of Datia. The other mantra that is referred to as mantrarAja is the nR^isiMhAnuShTup mahAmantra. Some observe that this title of mantrarAja or the King of mantras is valid only among the vaiShNava mantras and not in the shAkta circles. However, tantras like paramAnanda tantra, meru tantra and uDDAmareshvara tantra, in the context of shAkta dIkShA, refer to nR^isiMha mantra as mantrarAja. The prescription of the mantra is for the nivR^itti of duHsvapna doSha.
In our sampradAya, nR^isiMha anuShTup is accepted as the mantrarAja in the above context. I can think of three pramANas in this regard.
1. gauDapAdAchArya describes two sUtras in relation to mantrarAja:
a. vyomadahakarmavasupatrAtha hakoNavedAshrayutaM harimukhasya sadanam |
b. mR^igeshAsyasya ShaDiti (AvaraNa saMkhyA) |
By observing the commentary on the following verse from nR^isiMhatApanIya which describes the lakShaNa of mantrarAja chakra, it becomes clear that the mantrarAja referred to by gauDapAda is indeed the sacred anuShTup formula:
nAraiH patrairvaitatsarvataH parikrAmati |
2. There is an explicit uddhAra of the radanAkShara anuShTup mantra immediately after the uddhAra of mAlinI mantra in the paramAnanda tantra and the saMj~nA for this mantra is mantrarAja.
mantrarAja iti khyAtaH sarvatrAyaM sugopitaH |
3. The third pramANa would be the sampradAya. shrI harapanahalli satyanArAyaNa shastrigal was a disciple of H H Jagadguru shrI abhinava vidyA tIrtha mahAsvAmigal and was initiated into shuddha ShoDashI by the Jagadguru. He was given a copy of the AmnAya krama followed traditionally by the Acharyas of Sringeri Mutt and this copy lists nR^isiMha as mantrarAja.
satyaM paraM dhImahi