Not counting those that aren’t currently available or the regionals
Three that come to mind for me are onix, aerodactyl and electrabuzz
I finally hatched onix and aerodactyl during the Easter event
Electrabuzz eluded me the longest, I only ever saw one on the nearby but I wasn’t able to get to it. Finally with the most recent nest migration an electrabuzz nest formed about five minutes from where I work. I’ve only been able to catch two so far because it’s not a real active nest, but I hope to catch a few more because they’re decent for prestiging a gym.
It took me forever to get dragonite and tangela from Gen 1. I think it was almost Christmas before I got both. I don’t have amphorus or feraligator from gen 2. I do have enough candy to evolve both, just haven’t got a good IV to evolve.
Must be Porygon! It took me almost 7 months to hatch it, I never saw one in the wild (as probably many others), and overall, it’s the Pokemon I have seen the least since Pokemon GO launched.
All without the use of cheating to find it! Makes the feeling much better. I don’t see how it’s fun to just know where Pokemon spawn and how long left until it despawns
Mine would be Porygon (It took an egg hatch for me add it on my DEX), Togetic (I encountered one during “The Pokémon GO Eggstravaganza” it ran away and haven’t found another one. I don’t have enough eggs to evolve one either), and Onix.
I remember having problems with Muk and Kabutops. After Gen 2 dropped, I got everything in a decent amount of time due to buddy system and smart hunting.