ظَبْيٌ — nominative, ḍamma on the yāʾ.
ظَبْيًا — accusative, fatḥa on the yāʾ.
ظَبْيٍ — genitive, kasra on the yāʾ.
ظَبْي means “gazelle.” The bāʾ before its final yāʾ bears sukūn, so it is treated like a sound-final noun.
Be precise: not every word ending in wāw or yāʾ belongs here. The book specifically requires the preceding letter to be sākin.