I would concoct a potion to make myself invisible, allowing me to sneak into the dragon's lair undetected. Once inside, I would carefully observe the dragon's habits to determine when it would be asleep or away from the gem. Finally, I would seize the opportunity to take the gem, and discreetly exit the lair using a teleportation spell.
You are a wizard in a fantasy world, and you have to come up with a clever way to retrieve a stolen gem from a dragon. How would you approach this situation?