ньялис = nyalis.
this letter ь is called a soft mark. it softens a consonant before it.
я letter sounds like /ya/. and this letter softens a consonant before automatically
ньалис is incorrect spelling. ньа combination doesn't exist in russian at all i think. couse this sound combination is represented by ня = soft n + a. as you see /y/ form /ya/ is omitted here. /y/ appears only before vowels or at the beginning of a word. or before ь or ъ (hard mark).
in russian several vowels like я /ya/, е /ye/, ё /yo/, ю /yu/, (and и /i/) soften before standing consonant automatically but losting their /y/. to remove this softness hard mark is used - ъ.
ь and ъ force those я, е, ё, ю take their full sound forms - ya, ye, yo, yu.
ь and ъ create a break between sounds.
the difference between ньялис and нъялис is in softness of n. with soft mark it's soft with hard mark - hard. russian original way of pronounciation is to soften this /n/ in nyalis. нъялис sounds more unusual for russian language.
ниялис = niyalis
ниалис = nialis
нялис = n'alis (n' - soft n)
so the difference between ниялис and ньялис is in the length of i sound before ya.
in russian words й /"i short"/ often appears at the and of words. in original russian words there is no need in it in the middle of words, couse there are я, е, ё, ю and ь, ъ. but й is used in the middle of some borrowed words. sometimes there is no clearance e.g. mexican Yaxchilan is written by some people as Яшчилан but by others Йашчилан. there is no difference in sounds between йа and я, йо and ё, ю and йу, е and йэ there where full ya/ye/yo/yu sounds are used. but there is an advice of philologists to spell those sounds in a "russian way" with я, ё, ю, е. though i would say that in transliteration nowadays usage of я or йа, etc for some people is a matter of "beauty", but not of rules and advices.
нйа is not used it is spelled as нья or нъя. i find it diffcult to realize how to read consonant + й combinations. й usually stands after vowels.
p.s. i'm far not sure that what i wrote is complete or absolutely correct, cause russian grammar is such a grammar where native speakers can't be absolutely sure about anything
