Skin bug (not sure if it works on all champs, but Im aware of it working on Riven)
The bug occurs during picks. From what I have seen/experienced, if you pick a champ, say Thresh as I did and then trade with another one of your teamates, which for me was Riven, and then you change one of your summoners in the last few seconds before the game starts, you will be given a random skin that you don't own for the champion you are playing (my friend got championship Riven when we first found the bug, I got Crimson Elite). the skin will last the entire game but it will not be given to you after the game is over. I had to stop playing shortly after we found this bug so I didn't have time to test it on other champions, so hopefully you guys out there will be able to test most, if not all of them. I just wanted to bring this bug to everyone's attention, hopefully you can remove this bug soon!