About the game modeThis achievement is exclusive to the Winter Wonderland event in december (every year). Might turn up in the Anniversary event (different random events every day in May). It can be found in the Arcade menu, it is the 8 player FFA mode not the 6v6.
Rules of snowball fightEveryone plays Mei who has her wall and ice cube abilities from the main game. However she can only shoot icicles with a limited range and ammunition. One hit kills, the one who gets 15 kills first wins the game. Every player starts with 1 ammo and can get more by picking up (hold
or
) piles of snow randomly appearing on the map (max 3). There is an important new ability by pressing the melee button
: if someone shoots at you and you activate melee you can grab the icicle in the air and load it into your weapon. The ultimate attack is different as well: for a few seconds you can shoot as many icicles as you want with a greater speed. After the ultimate ends your weapon will be fully loaded with 3 ammo as well.
The achievementAs the achievement says you have to wait for anyone to raise a wall then damage it (one icicle destroys a portion of the wall) and finally kill them. You don't have to shoot them through the gap, you can go around or even attack from behind by shooting the wall then the owner even if it isn't in your way. While this is doable with 2 or 3 normal ammunition, your best bet is getting your ultimate as fast as you can then not playing to win but trying to force out the wall from someone. Waiting near two people who fight is a good tactic as well. Sadly if someone else damages the wall first you won't get the achievement even if you damage another portion. You have to break it first. Since everyone plays Mei it is very easy to get confused in larger battles and miss the real owner of the wall, this is why it is much easier with the ultimate.