Electabuzz/Electivire(not sure if the Pokemon will be able to evolve into their Sinnoh evolutions)
If there is Elekid in the Johto Pokedex, then so there will be the 4th Gen evolutions. Hopefully not like FireRed/LeafGreen, where you can only get the final Evolutions after the Nat. Dex.
You never know... I mean, this has only happened once before, and the other times, the evolutions have been included in the regional Dexes(RSE/DPPt).
I'm trying for a replica of Red's Bulbasaur... It doesn't want to give me the right nature... >_> I'm gonna have an even harder time with Poli, because it'll need the right nature and ability -_-'
