Mei is devastating at close range with her freeze guns, and if used effectively, she can make entire teams rage and want to just get the match over with so they can move on to the next. So let's go over his abilities and how to use them, so that you too can use her to this end.
Main Attack - Endothermic Blaster
Mei's main ability is the very short range ice blaster she carries. With the main fire she can hit anyone up close with a beam of cold that if she is able to keep the beam on them, they will freeze solid for a second or two, which gives her time to aim and fire the secondary mode of her blaster, an icicle, right into their head for the kill. Even getting hit in passing with this blaster can slow people enough for them to be easy pickings for your team.
Ice Wall
This ability, when used correctly, can be what makes a close fight an absolute slaughter. The uses of this ability are endless, but here's a few. You can cut a team in half bu placing this in the middle of them all and turning a six vs six fight into a six vs three fight for a few seconds, usually long enough to kill them and mop up the rest. You can cut healers off from their team. You can use it as an escape method. You can even use it to boost people up into the air by placing it directly under them, or you. If you don't use this correctly though, you could accidentally do any of these things to your own team rather than the enemy. Always be aware of how your wall is going to effect both your team, and the enemies.
Cyro-Freeze
This ability will take you out of the fight briefly, by encasing you in a block of ice. While in the ice you will heal, but be unable to be damaged or use any of your abilities.This can be good to use when help is on it's way, but you aren't going to live long enough for it to arrive. Pop yourself in a block of ice, and then break it to attack from within their team as your team comes in to assist.
Ultimate - Blizzard
Blizzard acts like Mei's blaster, but in an area of effect and with more damage. Enemies who stay too long in the effected area will be frozen solid, the same as with her blaster, and continue to take damage. This is not a high damage ultimate, but it can be very effective at immobilizing a team so that they can be easily picked off.
It does take some time to get good with Mei's abilities and learning when and how to use them so that they are the most effective. The most important thing to do to become a successful Mei player is to practice with her, take her into custom games with bots and practice your skills and most importantly, how best to use your ice walls. Otherwise, a misplaced ice wall can cause more grief for your team than the enemy.
Main Attack - Endothermic Blaster
Mei's main ability is the very short range ice blaster she carries. With the main fire she can hit anyone up close with a beam of cold that if she is able to keep the beam on them, they will freeze solid for a second or two, which gives her time to aim and fire the secondary mode of her blaster, an icicle, right into their head for the kill. Even getting hit in passing with this blaster can slow people enough for them to be easy pickings for your team.
Ice Wall
This ability, when used correctly, can be what makes a close fight an absolute slaughter. The uses of this ability are endless, but here's a few. You can cut a team in half bu placing this in the middle of them all and turning a six vs six fight into a six vs three fight for a few seconds, usually long enough to kill them and mop up the rest. You can cut healers off from their team. You can use it as an escape method. You can even use it to boost people up into the air by placing it directly under them, or you. If you don't use this correctly though, you could accidentally do any of these things to your own team rather than the enemy. Always be aware of how your wall is going to effect both your team, and the enemies.
Cyro-Freeze
This ability will take you out of the fight briefly, by encasing you in a block of ice. While in the ice you will heal, but be unable to be damaged or use any of your abilities.This can be good to use when help is on it's way, but you aren't going to live long enough for it to arrive. Pop yourself in a block of ice, and then break it to attack from within their team as your team comes in to assist.
Ultimate - Blizzard
Blizzard acts like Mei's blaster, but in an area of effect and with more damage. Enemies who stay too long in the effected area will be frozen solid, the same as with her blaster, and continue to take damage. This is not a high damage ultimate, but it can be very effective at immobilizing a team so that they can be easily picked off.
It does take some time to get good with Mei's abilities and learning when and how to use them so that they are the most effective. The most important thing to do to become a successful Mei player is to practice with her, take her into custom games with bots and practice your skills and most importantly, how best to use your ice walls. Otherwise, a misplaced ice wall can cause more grief for your team than the enemy.