Pikachu is a fascinating national phenomenon. I mean, within the Pokemon Universe, Pikachu has its own set of rules. Look at the facts:
-Kanto: Pikachu lives in the Viridian Forest and near the Power Plant.
-Johto: Pikachu is only found in Kanto-based settings, so Pikachu is accessible only post-game on Route 2.
-Hoenn: Safari Zone import.
-Sinnoh: Trophy Garden import.
-Unova: None.
-Kalos: Santalune Forest, Route 3.
Pikachu is only native to two known regions, both beginning with "Ka," which is meaningless. Although in Heart Gold and Soul Silver, Lt. Surge trades his French Pikachu with you, so this was likely foreshadowing or something.
The Kanto-native Pikachu has a sort of "dance" with the two other "P" Pokemon. Yep, Clefairy and Jigglypuff, (Pippi and Purin, respectively). This way!
-Kanto: All three native.
-Johto: None native; access in Kanto locations.
-Hoenn: Clefairy is not a native of the Pokedex (post in ORAS).
-Sinnoh: Jigglypuff is not a native of the Pokedex, can be found post (import).
-Unova: Pikachu is not a native of the Pokedex or region.
-Kalos: Clefairy is not a native of the Pokedex, can be found post (import).
Until Kalos, it was a perfect alignment. All, None, PiJi, PiCle, CleJi. Kalos throws it off, but hopefully the next region will balance it again. By the way, I chose these three because of Magical Pokemon Journey; plus they all have a semi-mascot status. Pikachu the top, Jigglypuff due to the external forces (anime and Smash Bros), and Clefairy the relic. Why these three? Why is it not that only Pikachu or only Clefairy has been a regional native? Probably a developer thing, I don't know.
So the main topic, Pokemon not native to their region. First, how odd that we never see any other Hitmonlee or Hitmonchan in Kanto. In fact, Tyrogue is only a gift from the same Dojo Master from Kanto. Hoenn has no Hitmon, although post-game in ORAS with the DexNav. Sinnoh might be the key, as Tyrogue are found post-game with the Radar. Or Unova; the first game has them in a swarm. Oh, the Friend Safari in X and Y!
But what is it with the Hitmons? They don't miss a region but they never have a home. Also, does it make sense that they hide so much? Listen to these entries.
BW: "It is famous for its eagerness to fight and always nurses injuries from challenging larger foes."
SS: "Even though it is small, it can't be ignored because it will slug any handy target without warning."
ORAS: "Tyrogue becomes stressed out if it does not get to train every day. When raising this Pokémon, the Trainer must establish and uphold various training methods."
These Pokemon are restless, instigators, and foolhardy. What sense does it make for Tyrogue and its ilk to hideout instead of rushing into battle headfirst? Nope, it's "Wiggle grass... wiggle grass... Bueller... Bueller..." I hope we see a Tyrogue-native region soon.
I don't know how much you can trust the Safari Zone. Did you know? Rhyhorn is not a native of Kanto or Hoenn. Both are found in their respective Safari Zones, and nowhere else. Cheap imports. Remember Gold and Silver? Rhyhorn is only found in Victory Road. Which is technically part of Kanto, ironically.
Finally, Sinnoh gave them a region to call their own. Oh, and Kalos has a RHYHORN RACER. Talk about publicity, huh? Meanwhile, Unova only allows Rhyhorn through White Forest or a trade with your Miley/Bieber popstar lover. What have we learned? Odd-numbered generations don't like Rhyhorn and try to make sure you don't get one easily.
Here's the thing, I don't really trust Kanto in general.
Eevee? Gift.
Porygon? Synthetic.
Fossils?
"Oh, sure! I'll accept this rare fossil from you for a few minutes and give you a revived Pokemon! Come back for it later!
...Okay, he's gone. Steve, get the Aerodactyl from the back room.
I don't care, any! He could be back at any time, and I need to rush over to Pewter Museum!
And make sure to fill out for a new shipment of Kabutos from Kabuto Island in the Zelpin region!
Oh, don't forget, we're meeting my parents at 6:30; they have a scheme they want to try, making trainers pay to have their Pokemon boink."
We know Kanto is overrun by crime, but maybe the crime here is the lack of culture. Think about it, how many are only gifts? By that, I mean all possible Kanto Pokemon given for free.
-Three starters, 9 family members
-Eevee, 4 family members
-Hitmons, 2 family members
-Fossils, 5 family members
That's 20 Pokemon right there.
In-game trade Farfetch'd "Ch'ding" (nickname for "Chandler Ding"?) is likely a native of sister region Johto. Lickitung also only appears through a trade. Oh and so does Porygon, a "trade" of gaming coins. What do we have, three more? 23? Hmm. Oh, Jynx. 24. Keep in mind, Japan!Blue has some Pokemon catchable. And Yellow. But what matters is the Red/Blue/FireRed/LeafGreen canon.
Sinnoh is notorious with this. Of the 107 Pokemon introduced, 29 are relatives of past generations, plus Regigigas, plus nine starters, plus two fossils. It's embarrassing.
That's why I like Unova. Many of the Pokemon have locations, nests and clear investment in the region. Not all, but there are zero relatives of the past, only two gifts, the nine starters (keep in mind, only X and Y have catchable starters), and the four fossils (discovery of fossils in a region does not mean the location of origin or nests). Unova has wonderful biodiversity, only trumped by Kalos. Although it has the Melting Pokeball aspect.
When only two years pass, the region floods with new Pokemon previously unseen. Why? Beats me. But it's better than Platinum. "Fire-type there, fire-type there, WATER WATER WATER." I think what a region needs to impress is culture, and that largely plays a part with its Pokemon.
Look at Kanto. We know NOTHING about its Pokemon of the past. Mewtwo is a clone, the birds are from Johto, Mew has a home in Emerald. With imports and whatnot, is Kanto really nothing more than a culturally void wasteland, where Pokemon need to be imported to impress? There's no tree-towns or bridges or three different dexes. No Gods or Demons or cultural traditions. In fact, by Gen II, the Lavender Tower, probably the most culture in the region, is turned into a radio tower. Genius.
It's soulless, and don't talk to me about "Oh, early on, they didn't know that Pokemon would go this far, so of course it's a dull region!" FireRed/LeafGreen made absolutely certain that the player's experience would be as identical as possible to the Red/Blue one. Know what that's called? Pandering. Like the Kanto region itself.
My theory is that Pikachu is their major export. To the Safari Zone in Hoenn, the Trophy Garden in Sinnoh, and to Santalune Forest to make it look like a"natural" habitat. But if they ever address the War Theory (Surge: "Pokemon saved me in the war!"), then I could end up eating my words. For now, I'll stick to the facts: There's 150 or less to see.