To create a super snowball, focus on a character's specific gem. You can either make a combination with these gems, or destroy them with special gems. A Yellow/purple line will start moving towards the right, once you destroy the specific gems. Once it is all the way to the right, your character will throw a super super snowball, and the line will start from the left again.
For anna/young Anna this is the purple square
For Kristof/ young kristof, this is the yellow hexagon.
Make a certain amount of combinations with these gems, and you will get a super snowball. This achievement might take some tries. The key is making a lot of gems with the other colors and as many special gems as possible, as this will spawn in more gems, including yellow/purple ones.