So I always run into this problem dealing with Gen IV pokemon, at first I can't find a PID that works, with it being flawless 6ivs and shiny using any method besides chain shiny. But, when I do use the Chain Shiny method... it forces me to have an unknown encounter type. For instance this Ho Oh, is from Heart Gold, Encounter type is set to in a building. Ignore the fateful encounter thing, it doesnt effect anything, i was just testing if changing that would do anything.
https://www.pokecheck.org/?pk=8913433