This is a singleton tag in the "character" category that, insofar as I am allowed to view, has no posts, though it's listed as having one.
It's in the wrong category, and there already is an ip:frogun_(series) tag, which is what this tag should be.
If someone could fix this somehow, that would be cool.
I couldn't find anything on the wiki about how to treat this issue, closest I found was "Changing tag categories" at help:tags, which I cannot do.
Nevermind, I went to settings and enabled "Show deleted posts". This allowed me to view the post.