Seeing that it's been almost a year...

It's Octillery! (Octazooka's Japanese name is Okutank (Octillery's Japanese name) Cannon.)
So let's try this again...
-It's native to the region featured in the most recently released games in the series.
-It has a pre-evolution and and evolution, but neither one was introduced in the same generation as it.
-A major recurring character in the saga of the anime that took place in the region featured in the most recently released games in the series has one.