Jump into the top left wind portal thingy.
On your way to the electric switch, there is a Gate that looks like its purple and yellow (you might percieve it as just a iron bar wall).
Use Cynder.
Use her SHadow attack, not the breath. Instead of just tapping the button, hold it down. You'll appear as a dark cloud. While holding that, you can pass through the purple/gold gates.
A large key will lower. Have Cynder jump onto the grass right next to the switch, then grab onto the bottom handle of the key.
Have spyro fill up the switch, then jump and fly all the way to the left.
That will lower the wall granting you access to the final gem.