The Department of Temporal Investigations from Star Trek. Individual agents can probably be neuralized (although there's probably some obscure species in the Federation that can't be), but they have a "shielded archive" that preserves other timelines that I don't know if we could tamper with. They're meta enough to know about the continuity reboot, and they're used to not asking about things they know they shouldn't know.

We generally shouldn't be having a lot of canon characters with PPC knowledge. It can mess with the whole modus operandi of "keeping the multiverse safe from threats it knows nothing about", and having the agents go into a badfic knowing beforehand that a potentially powerful character, in Pinkie Pie's case one of the main leads of the canon, is going to be on their side, seems to skew the basic set-up of hard-won victories and sanity only kept intact by snark and distractions.
Having Jack Harkness on the list is bad enough, since not only is he a main lead in Torchwood, he's usually immortal. Plus, I have no idea why he's even there. Does his brain heal from the effects of neuralyzation? That doesn't make a lot of sense, since the logical extension of that would mean he can't forget anything, and we know that isn't true. Whatever. There's too much precedent to remove him anyway, so... moving on.

A new canon character should really be added to the list if there are complications, for example if the character is all-knowing in-canon. Omniscience is a big complication, since it means the character can't be neuralyzed, which is why Aslan and Madoka are on the list. Doc Scratch, from Homestuck, would probably be up there as well, since he's not only nigh-omnipotent and omniscient, but he doesn't have any eyes to flash the light in.
Fourth-wall sight equalling knowledge of the PPC would make for a cognizant character in every third continuum or so, and since the fourth-wall-breakers usually tend to be less attached to sanity than their compatriots, that would create a scenario constantly on the precipice of spiraling horribly out of control. I don't think anyone would want that.

Pinkie Pie can be neuralyzed (pretty easily, come to think of it. "Hey, Pinkie, check out this shiny party favor!"). So, if she did find out about the PPC, which is totally possible, then the agents can just make her forget.

-Phobos