Last pokemon you realized existed

I know them all up until gen V, but from gen III I kind of forgot Chimecho was a thing.

Go is the only Pokemon game I've ever played so I'm learning as I go. If nothing else, Go has been a good way to help noobs like me identify Pokemon and learn about type effectiveness

In a similar vein, I don't know if I had ever evolved a Remoraid in any of the console games. If I had ever known its evolution, I had completely forgotten it by the time Gen2 was released in Go. Such a weird change. When looking through the Gen2 pokemon being added, I just assumed at first that Remoraid and Octillery were two stand-alone pokemon.

I only play Pokémon GO, I knew the type effectivenesses, but I don't play main series games.

Early in gen 2 I saw the shadow of a majestic looking bird in my nearby. I hadn't ever seen it before, it looked big, it had to be good, and I couldn't go after it. I was devastated that I had missed my (maybe) only chance at this ultra powerful, ultra rare Pokemon. Later on, I did find a wild Skarmory though. Then I hatched one. And another, and another, and another, and another.......