Hiay!
Overall, all Outer Planes beings should terrifying, like Old Testament angels. There is a reason angels that appear to mortals first say: "Fear not!"
Not sure if you have ever seen/used these...but Mayfair games put out a series of "AD&D" supplements (1e...this was back in 1993) called "Sentinels". It was a small boxed set that was part of their "Demons" line. The Demons line was just that...all about Demons; how they were 'organized', the power structure, special demons, demon lords, princes, princesses, and other. Absolutely AMAZING series! Anyway, the Sentinels box dealt with the "good" guys.
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I use "good" in quotes because they were more along the line of "The Cosmic Opposite of Evil"...meaning they only care about fighting "actual" evil...like evil gods, undead, demons, devils, etc. They, for the most part, see mortals as tools to use in their fight against the Demons. To this end...they do things with a "big picture" that has an outcome that is measured in centuries or millennia. Because of this, many seem...well...pretty freaking terrifying; it's a sobering experience to be conversing with an 'Angle' and be told in no uncertain terms that you are, for all intents and purposes, "bait". I mean, liked if not loved bait...but still....your pathetically short little mortal life will have virtually zero impact on the coming Apocalypse, and it's readily apparent that the Angles will use you, lie to you, and sacrifice you in a heartbeat if it will get them closer to winning when Apocalypse comes.
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Coincidentally, Mayfair also put out a boxed set called "Apocalypse" that covers just that; how to go about PERMANENTLY ending your campaign world in a Grand Finale! And no, I don't mean "how to run an apocalypse where the PC's can stop it"...you can't. Every PC dies. Period. Mind you, so does the entire Material Plane that the PC's reside on, so at least they won't be lonely!
^_^
Paul L. Ming