Check out the mini boss battle in the Battle Camp event, Into The Shadowlands, on all difficulties. If you are aren't sure if you can do it on a higher difficulty, check out this video and see what kind of fire power(pun intended) it takes to do all of them!
This video explains how to properly use the Swap ability on Battle Camp. It also describes a method you can use to become better at it. All mechanics and calculations behind Battle Camp gem-matching are explained.