Clash! Survival Snow Battle is the 15th episode of the Katekyo Hitman Reborn! anime.
All of Tsuna's friends show up at school during winter to help him babysit I-Pin and Lambo. However, in a turn of events, everyone besides Tsuna seems to just want to have a snowball fight, so Reborn turns it into another one of his staged competitions. Then, Bianchi appears and made it a 3-team battle.