HIGH Winrate and MMR so you can afford to lose a lot of games.
https://www.playerauctions.com/lol-account/137399659a!s8-euw-diamond-2-with-d1master-mmr-high-winrate-/
70%+ W/R so the mmr is really high, usually placed with d2-d1 in solo q.
https://www.playerauctions.com/lol-account/137259865a!s8-euw-diamond-4-high-winrate/