Using Celestial on the Oversoul to kill it super fast is a great idea, yes, but it's actually better to [i]not[/i] use it. If you down Crota, spawn the first Oversoul, then quickly down him again [i]before[/i] killing the first Oversoul, then just use your primary/special/heavy whatever guns to shoot down the OS, most of the time the timing will be such that he does not spawn a second OS. Killing it too fast with Celestial guarantees a second OS, which can be tense if you only have one golden gun. This way, people can use whatever they want without being forced into a "needed" subclass, and you only have one OS to deal with. I hope this helps some of y'all out there.