A stranger is a mysterious man who sometimes appears when players have a Diamond of Azzanadra in their inventory. He wields a dragon dagger and follows the closest person to him. He is non-attackable to the players not doing Desert Treasure, and attempting to attack the stranger when not doing Desert Treasure will yield the message, "He has no interest in fighting you." The stranger sometimes says "Master says hi," when he kills the player he is pursuing.
If using magic, use Impact to bind him and attack him from a distance. This strategy could also be used with ranged by using Binding Shot, but is less effective than maging him
If you don't want to fight, make sure you don't turn back. It also helps to have auto-retaliate off, so that you don't turn back, thus risking becoming hit and poisoned.
Have teleport tabs at the ready until you bank the gems. The stranger will not track your teleports, and therefore will not follow you if you teleport away.
Also, always try to keep all your diamonds in your bank for your safety. However, he can appear right after you get one of the diamonds, which can be annoying because you will probably have taken damage or exhausted Prayer from the fights. The more diamonds you have, the greater the chance for him to appear.
After completing Desert Treasure, the stranger may still appear. He cannot be attacked after completing the quest and will follow you about. If you move far enough away from where he started following you, he will lose interest and start following another person, even if they completed or haven't started Desert Treasure.
He can appear and attack you in the FamiliarisationDistraction and Diversion. You will fight with the same strength and accuracy as the weapon and the same defence as the armour you had when you entered the familiar plane but you will stay in familiar form while fighting.