What and how broad is your definition of a supernatural Aspect?
To steal from Justice Potter Stewart,
"I shall not today attempt further to define the kinds of material I understand to be embraced within that shorthand description ["supernatural aspect"]; and perhaps I could never succeed in intelligibly doing so. But I know it when I see it, and the aspect involved in this discussion is not that."
Now that I've got that out of my system, I'd say that devonapple did a good job of nailing down a pretty broad definition of "supernatural-themed aspect" which I largely agree with. Although for the discussion at hand, I would have a slightly more narrow definition for what fits into the Pure Mortal Template, because simply having a "supernaturally-themed" aspect doesn't kick a character out of the Pure Mortal club.
It's perfectly fine for a Pure Mortal's aspects to refer to
external magical influences. For example, Murphy has the High Concept "Special Investigations Lead Detective", which could be argued puts her frequently into the position of having supernatural stuff happen to her (nah,
really?!). And she has an additional aspect "I Don’t Know if I Trust Dresden, But He Gets Results" which gives her indirect access to Wizardry, which she frequently uses to gain information that another equally skilled investigator would never uncover. Yet she's Pure Mortal because they represent access to or a connection with the supernatural, without having any personal capabilities. Marcone is a "Freeholding Lord", making him a "supernatural player", and he has access to Gard's magic ... but has no inherent supernatural abilities.
So I'd probably encapsulate it this way: if the aspect indicates that there is something about
who the character is that is in any way supernatural, or that there is something about
what the character can do without the help of anyone else that is supernatural then it's a supernatural aspect and removes the character from the ranks of Purely Mortal. (Note that being the bearer of an IoP counts as being able to do supernatural things without the help of anyone else, but having a friend/protector/ancestor/whatever who can do supernatural things on your behalf does not.) This may or may not be a legally-watertight definition, in which case I refer you to the Stewart quote I mentioned above.
And as a further note, I'd like to stress that it is entirely possible and fair for a Pure Mortal to "borrow" supernatural capabilities without losing their Pure Mortal status. There have been a number of examples of this occuring in the novels.
And finally, regarding the templates and character sheets topic, I'd note that template is on the worksheet, not the character sheet, and that many people gloss over defining their custom templates. However, as I said before I believe that a character's High Concept must indicate that character's template (even if the template in question is a custom one). For example, Sigrun Gard is an "Honest-to-Odin Valkyrie" -- her template is "Valkyrie" which is a custom "Scion" template. When I say that every character needs a template, I don't mean that it must only be one listed in YS. (Kincaid's High Concept is not a good HC -- but was perhaps the best that OW's authors could come up with given the information Jim's given us.)