i think alot of pokemon from the hoen region that are not re-introduced in the later generations were forgotten
these include:
Surskit
Masquerain
Shroomish
Breloom
Poochyena/mightyena (get replaced by houndour/houndoom)
as for the rest, they were either repeated in later gen games or in the anime
these include:
Surskit
Masquerain
Shroomish
Breloom
Poochyena/mightyena (get replaced by houndour/houndoom)
as for the rest, they were either repeated in later gen games or in the anime