Jumping on the back of a crystal wyvern to tame it can be frustrating, as they are difficult to mount because of their height.

First, try approaching from the rear and hop on the tail. If you succeed, carefully creep up between the shoulder blades where the ride is most stable. Being further back on the tail or near the wings can cause a more likely fall. (Don't forget your parachutes!)

The easier option is to use a mount (like another wyvern)... to approach the tame and easily hop on it for the taming ride...set your own wyvern to FOLLOW and PASSIVE, SO THAT YOU DONT LOSE IT AND IT DOESNT INTERFERE WITH THE TAME. Good luck!