All the "cute" Legendaries
>Mew because it's only given out in retarded events, save for the one time it was actually in the games with Fire Red/Leaf Green
>Celebi because it's event distribution only, and not actually ingame without glitches and hacks
>Jirachi because it's never been in any game through normal means except a silly gimmick from Colosseum
>Shaymin because...well, it's forgettable.
>Meloetta because they just remembered the damn thing existed near the end of B2/W2's life
Plus the other Hoenn legendaries. No, I'm not saying TRUMPET REMAKE CONFIRMED, but all of the legendaries from Hoenn, save for event orgasm Deoxys, is only in games now as a joke or "bonus" unlock.
Give us better options to obtain these pokemon. I'm not saying a wifi distro for free level 100 shiny legendaries, since that's retarded as fuck, but an item that lets you battle and capture one from the past randomly per month. Like, based on your trainer ID, you could be facing Jirachi monthly, while someone else could be fighting Mew monthly.
It would promote trading, which is the main damn thing these games advocate.