moobeat on Twitter: "Champion Mastery chests (ability to get from S grades) has reset for season - timing bit off but was expected with start of new season"
Hextech Crafting, Loot system and Champion Mastery in LoL
Paladins: Champions of the Realm
LoL Mastery and Chest - LoL Mastery & Chest
Hextech Crafting, Loot system and Champion Mastery in LoL
Hextech Crafting FAQ – League of Legends Support
You can earn up to four chests each month, and each champion you play can earn you one chest per season." : leagueoflegends
Champion Mastery | League of Legends Wiki | Fandom
Champion Mastery for Android - APK Download
Loot Crate System for League of Legends Account Users
Changes Coming to Hextech Chests and Champion Mastery Costs in League of Legends | dbltap