Azkend 2: The World Beneath

The easiest level to complete this on is the very first level. Note that the conditions of this achievement must be met not only while completing the objective but also while bringing the medal to the bottom of the board. It is for this reason that I recommend using the Sextant passive item, which makes the object move down the board on its own. In this case, the medal will automatically drop to the bottom of the board once you fulfill the objective, eliminating half of your worry when going for this achievement. Your active item won't matter since you'll only be making matches of 6 or more.

To get this achievement, every match needs to be of at least six tiles to set off a ball lightning. You'll likely need to restart a bunch of times until you get a good setup, but once you do it's very straightforward and will only require a few matches to finish the objective. The medal will then drop down on its own and you'll unlock the achievement when the level finishes.