"Once you have found the Negg stash for the day, Kari will let you choose a Negg from three special-themed options. You'll then receive one of three possible prizes from your chosen Negg! There are 5 different themed Neggs that you may find throughout the event. Each time you find the Neggs, Kari will randomly choose which three to offer you—so choose wisely.
This is also true for Premium Members. However, thanks to the Premium Extra Prize Perk, you will also be granted one of the three Premium Prizes from inside each Negg! So for each Negg you choose, you will receive two prizes: one of the three regular prizes and one of the three premium prizes!"