While it was possible to skip Iron Island (until you needed to fill out the sinnoh dex) and Riolu by extension in DPPt, if you ever wanted to get one yourself it was rather easy to do so thanks to Riley giving you an egg for one.
Zoroark and Zeraora aren't easily obtainable thanks to them being locked behind events, meaning that if you ever wanted to use one in their source generation you either had to get that event while it was active, or cheat them in.
>>46061170I think Game Freak forgot everything about Kalos aside from Megas and Zygarde.
Also, weren't the Kalos mythicals revealed after ORAS's release?
