Master Skins
When the champion mastery system came out, I was really excited. I would finally get to show everyone how much of (champion) I played. They would know my experience on this champ and that I knew what I was doing. It felt like I was off my time spent on a champion. But you wanna know what actually happened when the mastery system came out. I got a new emote that I could spam after killing someone or dying. I got a new tool for BM. And as much as I love spamming my emote after winning a duel with a fed riven, I wanted more.
Now I'm sure many of you have heard of this game called Heroes of the Storm. (I think they are in Smite, too!) And if any of you have ever played it, then you would know they too have a champion mastery system. You get periodical rewards from playing a lot of one champion like in-game currency and portraits and the like. But the biggest prize you can get, the most sought after items in the game, the best thing you can get from the mastery system is Master Skins.
These are exclusive skins you get from hitting rank 10 in on a champion (about 75 games) and then buying them with a hefty amount of in game currency. Now these skins are not extremely flashy, no where near as fancy as out legendary skins. I would put them on the same cosmetic level as chroma-skins really. But its not about how flashy they are. Its about being able to show that you put in the time in a relatively meaningful way.
I like the way the mastery system currently exists. The free emotes are cool. I think that Master Skins would improve the system and really add much more progression to the whole system.