Turns out that mastery isn't a free level 12 upgrade for champions, this reward is probably more efficient as 40k gold after two book of books : r/ClashRoyale
How Champion Mastery Works in Legends of Runeterra - Legends of Runeterra Guides - Out of Cards
The Complete League of Legends Mastery Overview | GooseSmurfs
How Champion Mastery Works in Legends of Runeterra - Legends of Runeterra Guides - Out of Cards
How to Get Mastery Level 7 in League of Legends? - LeagueFeed
ALL CHAMPIONS RANK 7 | The HIGHEST MASTERY SCORE in League of Legends - YouTube
Sad to be stuck in silver with this mastery points : r/RenektonMains