DON'T do public events because someone can steal your kill at the … Fallen Public Events, which take place on Earth and Nessus a lot, are a great place to find Powerful Fallen enemies.
Kill them all, then climb up the wall here to reach the crashed ship where Xur sometimes spawns. He spent his younger life studying the laws of physics, even going so far as to complete a PhD in the subject before video game journalism stole his soul. The first two waves of enemies will have Powerful Dregs, and lesser enemies, that are very easy to kill. After they are dead, a Powerful Captain will arrive, adding another notch to your belt.
