The Double Snake is one of the most difficult crystal critters to obtain in Dizzywood. It is hidden behind two rocks in the Theta Potato Mine (the second mine).
First you go to The Crystal Catacombs to enter the Elder Vein Mines (don't forget your Mining Helmet), there you must collect all three pieces of the Corrupt Crystal Dampener.
After you have found them, make your way through all the mines again to get to the Theta Potato Mine.
Use the Ghost Ray power to locate it. You need to use the power on a rock and then quickly use it again on the second rock behind it to reveal the Double Snake (see picture).
NOTE: Kan the Geomancer in The Explorer's Camp can reanimate the critter for you.
NOTE: Make sure to feed it a wink emote every once and a while!