Gryphion

First off, I'd like to mention that I'm nowhere near the point where I'd like to delve into "competitive" play but I'd like to be informed either way. My main question is, when trying to get a specific pokemon, how do you rate the importance of IV's? 1. Is 31 in the 2 main stats the minimum requirement or can you be satisfied if they are, let's say, 27+? 2. Do you take into consideration, the total amount of IV points? 3. What would be the minimum for the non-main stats? 15-20? 4. Is having below 10-15 points in a non-main stat a big weakness or can you work with it? This is all considering the fact that it is just for PVP in PRO. Not any real competitive tournaments out there.