It's just a free fan made game, if you ever played a pokemon game before like red, yellow, blue, and such before the 3ds it's like that, it features custom pokemon created by the devs along with some familiar pokemon, I have personally only seen three myself in that regard, mankey, dunsparce, and magikarp.

It's set in a new custom made region with a new story and new types, many of the pokemon I have seen thus far are super cute, even the starters are super cute <3, one that you can find early on in route 01 is called cubbug it's like a cross between a caterpie and a teddiursa, it's a little bear bug of cute, named mine cuddlebug ^w^

It features online play, for trades and battles, as it stands you need to exchange trainer ID's in order to battle or trade, they have a wondershare system that allows you to trade with random people though.

All in all it's basically another pokemon game, just for PC rather then gameboy or 3ds, it's free, and the devs are still working on improving it, hence the patcher that if you download you have to do a bit of a quick fix for to get it working as intended to download patch fixes.

All in all if your looking for a pokemon game to keep you busy for a time and have reliable access to a PC you should grab it and give it a try, you really don't need the internet for anything other then downloading the latest patches and doing the optional online stuff that is located at the pokemon center like it normally is.