User blog comment:N1ghtSt0rm 22/Just Some Questions An Experienced Noob Has.../@comment-24946635-20140812003052

I can step in on #1. I agree with what people have been saying about all points, but I feel like #1 hasn't been talked about much.

League already breaks down champions into categories pretty nicely. There are notable exceptions which don't break down well, but very few, even with few categories. Over time, these categories have been very well hashed-out in their relationships to each other, and it's gotten to the point where there are minor categories within the categories. For example, burst mages and dps mages.

Categories are determined almost 100% by abilities and the amounts that you have of them. A lot of low cooldown spells that dish out magic damage = dps mage. A passive that gives you additional CC reduction + a dash that deals physical damage = fighter.

New champions are released with enough of this information to know how they work, even when we haven't seen it in action. In Gnar's case, the biggest information was that he has rage as a resource. There are only a few other rage-based champions, and they are all fighters or junglers. Once you add in the information about his abilities which was released, anybody who cares about categories and such can pretty much nail down Gnar's lanes, category, and mini-category, and thus can tell where he fits into the Rock-Paper-Scissors-Lizard-Spock of League.

Which is, in sum, why people can know that certain champions will counter him, even though nobody has played him in regular or ranked games.