After the Robin Hood on Ice incident, Snape is described as looking "as if he ever found out who the perpetrators of this act, they would beg for something so sweet as having their heart cut out with a spoon".
I Just Write the Thing: The author openly admits that sometimes characters surprise him — notably, he says that the blooming romance between Uhtred and Jean-Paul took him entirely by surprise.
He even commented that he never planned on Harry/Carol to blossom the way that it did. The fact that it did took him off guard.
He openly admitted that he was surprised at how Harry Dresden & Wanda Maximoff got together in Chaos Reigns.
Name's the Same: Lily Potter and Lily the Summer Lady. Harry notes this, and is very glad that his reaction to memories of/thoughts about his mother are not the same as his Distracted by the Sexy reaction to Lily the Summer Lady.
This is also invoked in the case of Harry Potter and Harry Dresden, who are really quite similar in several ways.
One of Us: The author namedrops TV-Tropes several times, and has even mentioned involvement in the fic's tropes page.
Trolling Creator: The author was asked repeatedly for Harry's animagus form. The start of Chapter 23 announced that it would be revealed at the end of the chapter. It turned out to be Captain Jack Harkness. Readers were then informed that yes, he [the author] had lied and they had best get used to it.
In response to a WMG theory being put forward that Strange is actually a future, time-travelling Harry, the author specifically said that that was originally the plan, but was cut for being too complicated (which, considering his Complexity Addiction, is saying something) and actually depressing to write.
Word of God: Present in the rather extensive (and somewhat snarky) A/N's at the beginning and end of various chapters that serve to clarify and expand points raised in the text.