The Moss Key Pin is a Pin that was released in March 2010. This pin is the only way to enter the Underwater Room from the Hidden Lake other than during the Cave Expedition. The only way to get it is from inside the Underwater Room but the only way to get in there and do it is by playing the game Puffle Rescue.
The only way to find this pin is to be in the Underwater Room however it is impossible to get into this room without the pin unless the penguin plays the game Puffle Rescue.
In the game the penguin must play the, members only, Black Puffle rescue one and, after getting the black puffle, the Giant Squid will appear and swim out to sea leaving a trail of bubbles behind it. The penguin must use those bubbles to chase the giant squid to a coral reef far out to see where there will be a staircase which leads into the Underwater Room where the penguin can get the Moss Key Pin.
Spoilers end here.
Trivia
If Puffle Rescue stays, then this could become the second ever permanent pin. (The first being the Captain's Quarters Key.)
