It’s possible (though perhaps unlikely?) that you were thinking of this old thread on killing Ravager
Idk, that’s the one that comes to mind for me when I read your description. The thread is somewhat dated, though, enough so that Ravager’s AI behavior changes from the patches mentioned at the beginning of the thread to the patch mentioned at the end. Of course, it’s also directed at Ravager in particular and perhaps you were thinking of a more general thread on celestial hunting.
Hopefully, someone will come along with a more satisfactory answer with respect to finding the specific thread, but in the meantime, a sort of half-solution might be to search the name of the specific celestial you want to kill in the “Classes, Skills, and Builds” tag and take a look at some of the builds that pop up. A number of build threads do briefly address performance against celestials and occasionally even offer alternative (i.e. more defensive) specs for particular situations.