Table of Contents
Celestials
Celestials for the sake of this campaign setting are what the 5.5 Edition PHB refers to as “Aasimar.” We're not going to use the term “Aasimar” at the game table simply because the Dungeon Master hates pronouncing it and is a grumpy older1) guy who detests this much variation from the races2) that existed as standard playable characters in earlier versions of D&D.
Campaign Definition
Celestials are the flip side of the coin to Tieflings. Instead of being based on demons/devils, they're based on angels/heavenly type lineage. For our purposes we will say there is a broad range of things from the heavens that would also count as being in the Celestial category. The general vibe however is that a player character being a Celestial is a humanoid that to paraphrase the core materials carries a spark of magical lineage from greater Celestial entities, via bloodline usually. Note that in a completely sterile core setting there'd be chatter about the “Upper Planes”, which we are not defining or even acknowledging as existing at this time.
Other Celestials
There are several official Celestial branded creatures in the 5.5 edition Monster Manuel. This includes things such as Animal Lords(demi god like figures), Giant Elk(just an awesome bit of improbable nature), Sphinx's and Unicorns to name a few. Which means for the sake of this campaign setting there is at least the noteworthy Socks the Unicorn.
Player Character Use
For our sake just use whatever stats and abilities belong to the “Aasimar Species” in the PHB and write it down as being a “Celestial” as not to annoy the Dungeon Master. We'll also go ahead and say player characters as Celestials enjoy a lifespan about equal to a humans, have the general physical features described in the Players' Handbook, but subject to slight input and debate, and we'll accept them otherwise as is. Let it be known however they are a minority race so far in the campaign setting.3)