1. I have got (only once, but happened) my whole super back with a well placed Nova. I was using shatter and bloom. You could be right about one death (regardless of tyhe enemy´s rank) giving you 10% back, I have thought the same, and I´ve been using the Obsidian for a while (got it almost a month before Xur sold it. Not saying this to be an "earner"wannabe, just to point out that I have used it longer than others and have observed & experimented more. 2. I don´t think so, because although it´s a modifier for the Nova, it doesn´t register as a kill from the Nova itself. My set for the nova is Angry Magic+Shatter+Bloom because I wanted to use my Nova as a crowd controller move to take down (or damage) huge mobs of enemies at once. This setup has given me the best results of all setups so far. Last but not least: Bad Juju. Give it a try. As some others have said, it also gives you extra energy per kill, so you will be getting extra energy from the Inverse Shadow perk in the helmet, AND the String of Curses perk.