Snow Firefly Nest (ユキホタルの巣, Yuki Hotaru no Su) is an event in Tomba! 2: The Evil Swine Return.
Catch all of the Snow Fireflies in the nest found in the Ranch Area.
Climb to the highest ledge right above the nest (requires the Grapple), and push down the bolder. It will destroy the nest and 5 fireflies will fly out of it.