This is my first main pokemon game after PoGO. At the cemetery of the first island, i encountered a shiny ghastly (not SOSed).

You know that guy who ask for a haunter for a graveler in island 3? I was hesitant to gave my shiny now gengar to him so i evolved another ghastly in Tapu Village. Comparing those two, the latter has better typing and better status even one level below the shiny. So gave that NPC a shiny one instead. Since i thought the normal one must be have better IVs and even better typing will benefit me in the long run since there's no way to change nature of the shiny (am i right?)

Continuing the story next is hunting Mimikyu on Acerola trial. Gengar is everywhere and caughtable. Now i kinda regret it, at least i could wondertrade it to someone instead.

To makes things convenient in the future i spent my last 4 days hunting and breeding Abras until i got all different prefered nature and have synchronize ability. From top left to bottom right: Adamant Impish Careful Jolly. Modest Timid Bold Calm. Brave Quiet Relaxed Sassy. Next is hunting exact Dittos with those Abras.

TL;DR: gave a npc a shiny pokemon, proceed to a story theres plenty of pokemon the npc want.