From the Super Mario Wiki
Frosty is one of the Snow Spirits found in Mario & Sonic at the Olympic Winter Games. After Bowser and Eggman captured the snow spirits, Frosty managed to escape and ask Mario and Sonic the Hedgehog for their help to rescue his friends. He has been around with the whole cast, until Bowser and Eggman captured him in a cage after Mario and Sonic freed Blizza. In Blizland, his cage was guarded by Dry Bowser. While Mario and Sonic challenged Dry Bowser in Curling Bowling, Blizza tried to free Frosty, while Toad supported Blizza. When Dry Bowser lost, Frosty was freed.