Gen 4-6 first encounter

I dunno if this counts, but I found a Drifloon while soaring! One of the first times I went soaring, well before the E4. I was pretty shocked.

That was the first (and as of now, only) Pokémon I found in the wild not native to the Regional Pokédex as far as I know.

 

I stumbled across some Dexnav Pokémon in Shoal Cave while I was looking for the normal Snorunt, Spheal, etc, as well as working on the Slowbronite. I didn't even have the National Dex, and guides assured me that I needed that first.

 

I stumbled upon gothorita as I was dexnaving for Ralts a while back an boy was I surprised.

 

I found Sewaddle after I defeated the Elite 4 the first time around in Alpha Sapphire. I was confused... But caught it all the same.

 

I found a Lillipup on the first route after receiving my Johto Starter, so that's pretty cool .

 

I think my first encounter in ORAS that wasn't from the original Hoenn dex was Reshiram, haha. And that was when I was soft-resetting for a shiny one, so technically my first encounter in that regard was a shiny Reshiram. If you don't count that, I remember running into a Zorua on Route 101 and being kind of surprised that it was just in the wild like that, haha.