I just spent 2 hours of googling "how to get big mastery 7 emote" just to realize that the lower the resolution the bigger the emote : r/leagueoflegends
Riot dev reveals plans to expand League's Champion Mastery system - Dexerto
dev: Your Eternals Feedback in Action - League of Legends
Apparently the Eternals Mastery Emote upgrades 3-5 are in the game files : r/leagueoflegends
League of Legends Mastery - A Complete Guide - LeagueFeed