Pretty self explanatory. They don't have to be all in one rage, just in one match. Here's some tips.
- Drop your shield behind you as much as possible. Especially when the Meis are chasing you.
- Watch for traps of course. Getting stuck in those could prove fatal.
- Don't be afraid to use your gun when not in rage mode to kill a Mei. It'll melt her pretty quick and some players either don't use their ice heal right away so you can kill them or use it before you get there and it hasn't regenerated in time.
- When you have 3/4 meats, get to the last one and kind of wait a second in an attempt to lure Meis to you. Sometimes players will be stupid enough to come toward you and that's when you get them.
You have about 15 seconds or so in rage mode. It can be hard sometimes to keep track of where the Meis are when you're constantly flying around in rage mode. Don't panic though. You have all match to simply kill 3 of them. Obviously if you kill 5 of them, you win, so just aim to win the match in general and this will come easy.