One of mine is Hawkmoon and Vex dropping simultaneously from Atheon. I took a screenshot of it. (Incidentally, how do you attach photos through the app?) Also, Gjallahorn from Omnigul. But nothing beats the first time Hawkmoon (pre-nerf) dropped from Archon Priest nightfall. Almost broke my headset as I flew out of my chair. Those feelings are gone since Y2. My luckiest RNG was Thunderlord dropping from a random loot cache on Rocketyard while patrolling Cosmodrome. Didn't even know what an exotic was at that time.