counterpicks to master yi are generally champions with point and click abilities, the key to beating that strategy is to chain cc and have your own diver on the team to attract some attention while you do said cc chaining onto him, some of the better picks into yi for mages would be
they have abilities that are very difficult for him to alpha strike dodge, forcing kayle to burn her ult early, or him to buy a qss early, which is 1300 gold spent on that
that strategy requires coordination to defeat, as it's a duo setup which means you need atleast one other to beat it, in the end its a team game so that shouldn't sound to bad right? ugh...