What I think defines someone mastering a champion.
To prevent criticizing someone else, I'll use myself as an example for this. I main Kha'Zix. Keep in mind this post is my opinion.
#Games Played Does Not Define Maining/Mastering a Champion https://i.gyazo.com/522dae21bff0f49d7fbf6d4cd4fd8d16.png
The amount of games you play on a champion does not speak that you main/master them. To me, a champion is more than just playing them a lot. In time playing them a lot can translate to doing well on them, but pure volume of games isn't evidence since there are people that could play a champion 100 times and not even know their passive.
#Champion Mastery Does Not Define Maining/Mastering a Champion https://i.gyazo.com/de3b6ab77784ea626c27c40c9c83fbce.png
This is debatable. There really isn't a perfect way to automatically rank how good someone is on a champion, so it's not Riot's fault that the Champion Mastery system is sometimes flawed. People can argue that things like CS or objective control aren't specific to champion mastery, and you could argue the opposite. The fact of the matter is, however, that having a really good game on a champion every once in a while, which got you rank 7, shouldn't be taken as a reason you main that champion. The end answer is that this isn't a viable way to show that you've "mastered" a champion.
#Rank/ELO Does Not Define Maining/Mastering a Champion https://i.gyazo.com/4bf105a12af875221b43d934b636abca.png
This should be self explanatory, but I'll bring it up anyway. For myself as an example, the fact that I am in a "above average" rank and play Kha'Zix mainly does not mean I am a main of his. Being good at the game does not directly translate to being exceptionally good at a champion.
#Skins Does Not Define Maining/Mastering a Champion https://i.gyazo.com/936b28c858207a08c6898e04b317b7ad.png
Again, very obvious statement, but for those of you who aren't aware, having cosmetic content for a champion does not display skill. However you look fucking amazing amirite.
#What Does Define Maining/Mastering a Champion? Consistent Performance. https://i.gyazo.com/7665d5d919a1b61fc24fe164d33061e0.png
This is what really means you've mastered a champion. Like the other examples, it's subjective. If you are smurfing or belong in a much higher skill level, it's different. But when you can consistently perform above other players in your MMR who are playing champions that they either play moderately or main, I feel like this means that you have mastered your champion for your individual situation. You could argue if you truly master a champion it would carry you to Challenger, but that's individual skill. Champion mastery is based on your performance.
I don't know how much discussion will come from this post, but as a fore-warning this is not a "Kha'Zix is OP thread" so please do not argue such. Certain champions do better at different ranks, and the fact that I can crank out Kha'Zix normal game wins does not mean he is over powered.
Thanks for reading. Now go out there and master your champ.
with his steel legion skin, I somehow out-perform my playing ability when I don't use it. Needless to say, it's not particularly hard to go god-mode with
tho