Hammerfest King

Effect: "You finished the game! Your perseverance and tenacity permitted you to defeat the evil Tuber and to recover Igor's nose. From now on you'll have an extra life and you'll play with the carrot!"
Tuber's successor
Effect: "It seems like Igor has... changed. His look has become cool. He hides behind a great cloak and his face is dark. He's maybe changing little by little into the monster who was once his enemy. Disguise Igor as Tuber by pressing "D" key during the game!"
Empty Tuber's pocket
Effect: "Tuber, the evil sorcerer, used to have a key..."
Nightmare mode
Effect: "You're talented. Very talented... but, are you able to help Igor in the Nightmare mode? This new option has been unblocked!"
I notice a few people that beat Tuber before me had three Ice Cream Keys. I know that one is from defeating Tuber, one is from beating Tuber in Nightmare mode but what is the third key from?