Soda Dungeon 2 – What Is Character Mastery XP? How Do I Get More of It?
Mastery XP is earned at 1 per floor, per character in your team. So if you bring 5 soda junkies, they will get 5 XP per floor. Later on in the game, you unlock a mastery relic that can increase this by up to 10%, and you can also craft Triangle gems (recommend waiting till the last dimension for these) to increase the mastery XP gained by 10% per gem. This bonus applies to the whole party, not just the character carrying the gem.
Characters unlock additional abilities at level 25 and unlock a relic for that character at level 50 that adds +2 attack, hp, and mp per rank in the relic. You can see all of the benefits gained from mastery by clicking on the character’s portrait in the character section of the stats book (upper left corner of your screen).