Snow was introduced to Transformice as part of update V0.124 and was removed in update V0.129. Snow occured randomly in levels to help celebrate Christmas. It stopped after 5 to 10 minutes.
Anyone with the "Can load a map" permission in a tribe can make it snow in the tribe house by using the /neigechat command.
During the snow, mice could throw snowballs at each other by pressing and holding the ↓ key or S key until the snowball was thrown. This action replaced the mouse’s duck animation.
If a snowball hit another mouse, the snowball acted as a spirit but exploded much like a bomb, thus causing mice to go flying. They could move NPCs.
Sometimes it could glitch anchors on objects.
Though well received by most, some mice complained that this new feature aided trolling. If you were feeling very nasty you could also troll the shaman.
Note that when snow no longer filled the background of a map, no more snowballs could be thrown and those on the ground at the time lost their ability to explode. These snowballs could be moved around by mice and were slightly fun to play with.
Although unknown if intentional, snow would still fall downward on upside down maps. When it snowed, in Room 801, the snowballs did not explode and if you hit Papaille or Elise with snowballs, they would move. You can make your tribe house snow by using the /neige command.