The Winter update for Overwatch saw the release of several winter themed skins for various characters. One of the legendary skins was for Mei. However fans expressed their disappointment at the quality and the aesthetics of the skin. The skin which costs around 3000 coins is not easy to obtain, but some feel it is not worth the price. The reasoning for naming the skin a legendary skin, according to Jeff Kaplan was because they completely redid the visual effects for Cryo-Freeze ( Snowman effect).
The current criteria for categorising skins into legendary is not fixed. It is based on the developers own instinct. It can be safely said that the developers were wrong on this instance.
Hi there. Sorry you are disappointed with Mei’s winter skin. We don’t have a specific rule for what makes something Legendary or Epic. We just sort of make a gut call based off of what we think is cool. Coolness is very subjective, and based off of the community reaction it seems like our gauge was off on this one. Our reasoning for it being Legendary was that we completely redid the visual effects for Cryo-Freeze (we turned the ice block into a snowman). We thought that was pretty special and we had done it specifically based on community suggestions from months ago when people were speculating that we might have a winter event. Apparently, lots of people don’t agree with us and that’s ok. It’s all good feedback and we’re learning something for future events.
For people concerned that Mei is not going to get another Legendary for a long time, you need not worry. We have something pretty awesome for her early next year.
Apologies that our “cool meter” was off from yours on this one. We’ll try to align better on future content.
Source – BattleNet Forums