Well, I have noted a lot of people trying to find the key. I decided to make this tutorial or whatever you want to call this. If you want to find the key to get to the underwater, read on!
1. Go to puffle rescue.
2. Select the black puffle levels.
3. On the first level, go straight ahead and find the black puffle.
4. Continue on with the puffle, using the air bubbles emitted by the shadow of the squid to stay afloat. Be sure to bounce off of every single bubble or you'll drown.
5. After a few bubble-to-bubble hoppings, you'll reach a reef.
6. Follow the maze of the reef.
7. Eventually you'll find an entrance.
8. Swim over there and click enter on the window that pops up.
9. You'll be in the underwater room after you click enter.
10. Pick up the key pin and then you'll have access to the underwater room without playing puffle rescue!
Hope this helped for those of you that needed it.
