Spinda. Believe it or not, I was near bewildered when I first met Grumpig - at a Generation 4 Battle Frontier match. Not even Gen 3. It took me a long time to realize that Spoint evolved into Grumpig, and that they were both from Gen 3... I still forget them as well.
I also forget about Remoraid. And Corsola. They're really hard to meet in the first place, anyways... (unless you get them by trade?)
Smeargle. I always forgot about him till now.
My favorite shinies. :3
I actually have a pretty good memory of all the pokemanz, but some that I really have to say the name over and over are probably some of the gen V. Odd thing is now I keep forgetting Mawile exists. It used to be one of my favorite pokemons, but somehow that got lost in time...
"At noon on Wednesday, i'm gonna be leaving a watermelon-pineapple treasure inside of Liam Neeson. He's the one with the cooked fish allergies."
There's this site called sporcle that has these little quizzes that you can take. I do alright on most of them, but I can never seem to remember more than 65% of Gen II. So there you go, 35% of Gen II. I'd tell you the names of the pokemon, but I kinda forgot them.
A remoraid, maybe. Keep forgetting.
Cressalia, strangely enough. I'll go through my boxes and be like, "What is that?"
Spinda i forgot about comletley i find it pointless if it wasent for platinum swarms i still wouldent rerember it.
alot of the hoenn dex fillers i forget since its been the longest since i went to hoenn.
these 2 i forgot existed for ages but i now love both
pinsir i just completly overlooked for years somehow when scyther or heracross come to mind i forget the other beetle, it is so awsome i somehow forgot about how strong it is omg finally using them now !!
paras/parasect not only forgot they existes but forgot they were bug type aswell !! i love them now, they deserve plaudits.
Lol if I forget it exists how should I answer you
But reading the first few posts, I would say the Spoink line.
For the longest time I didn't know what a Dunsparce was.
A lotof Gen III seems forgettable to a lot of people here :P