So, I count this as a glitch as obviously this is not something the game intended you to do, but basically you can kill Wing during Fear of Rain while hes stuck in the cutscene not moving. Basically once he starts talking you are locked out of moving, but for whatever reason the designers of the game never bothered to lock you out of throwing grenades. If you accept the mission from a far edge then you can just barely lob grenades over the middle of the cathedral and hit wing where he spawns. As long as you don't complete the text he will just sit there and you can get your four hits in one at a time, with a small wait in between each one for his invulnerability to drop. I will post a video of it soon on my youtube, but its on my World Record Any% run.

Madknight Pash

Here is a video of me showing how this works: