In this guide is explained how to get all the secret achievements of the game
I Found The Developers
There is a secret Dev Room on an invisible island. Just go to the NPC island and use your jetpack to jump off the middle left edge of the island. You will jump to an invisible island. There is a hole on the island that you can go down to talk to the developers and get their skins.
To fly on a moshy you need to have the Moschy saddle. To have the Moschy saddle you must have beaten the Moth Boss. After you need to return there and drop a mutated blood flower on the rock. And after enter in the room and open the chest.
Difference between a blood flower classic and a mutated blood flower