OW Hero: Mei

A good Mei can make a Widow's life very difficult, with well timed ice walls to stop them from picking off your team. Her icicles are also very easy to land on a scoped widow and do a ton of damage.

As widow, if mei get's close grapple away before you get frozen, and then unless you are very confident in your aim, try to use your assault mode instead of your sniper mode. If you scope in Mei will easily finish you off with icicles before you can even get a full charge, whereas she has a higher chance of missing her projectiles if you use assault instead.