That Amumu buff was incredibly ill-conceived.

Turning him into an aoe true damage machine that can share that true damage with allies while he's already highly durable with great cc was simply a terrible idea. Both his winrate and playrate spiked several percent within days of the patch hitting. Normally a large increase in playrate comes with a decrease in winrate as it means more inexperienced players are picking up the Champion. When both jump up at the same time, it means the buff was just a terrible idea. Especially considering Amumu wasn't "suffering" like Riot seemed to think he was in the patch notes. This buff was way off base and is entirely too strong.