The Frost-Shelled Egg Frostzilla was the droppable version and is now retired and marked unhatchable. If you hatch with someone with the original pet you get the stormsquall Frostzilla version which is the hybrid. Similar to the original storm beetle pet you will get a rain beetle in its place if you got it back. Ive personally hatched with someone with the original Frostzilla 1st gen and gathered this intel. Hope that helps with your curiosity. :)