جَاءَنِي مُسْلِمِيَّ — nominative subject with estimated wāw.
رَأَيْتُ مُسْلِمِيَّ — accusative object marked by yāʾ.
مَرَرْتُ بِمُسْلِمِيَّ — genitive after bāʾ marked by yāʾ.
Principle: do not determine the case from the final sound alone. Identify the governing element and syntactic role first.