Adera

In the Jungle Cavern there is a mini-puzzle that requires you to hit the blue/orange rings, squares (the ones you have to drag along a path) and little diamond shapes.

When you tap the diamond shapes, a couple of bubbles will come out (Usually 4 or 5). To get the achievement, simply tap 20 of those little bubbles. It will unlock as soon as you hit the 20th bubble, so if you're only one connection away from completing the puzzle and you haven't gotten 20 bubbles yet, just fail a couple of rings/squares and wait until you get a diamond again.