In short? Nothing! We don't know anything as far as weaknesses go. We can make assumptions based on past experience, of course, while going under the assumption that our mutual Tallish Friend has an aversion to lying about HHIZ capabilities. You don't need to speak false truths to bluff.
The bluff metaphor is oddly appropriate, actually.
Remember when I said this was a game? I didn't mean one that we're playing. We're just the toys.
But perhaps even extradimensional thought-constructed non-entities have a concept of gaming, fun, and rules? Even if TPF is actually invincible by human standards, limitations could be set on the Tall One's game, by HHIZself.
... Okay, phonetically, that sounded like some half-retarded attempt to sound 'gangsta'. My bad.
Back on topic, it just means one needs to take advantage of them before TPF understands cheating as well. So just to pick out a few of these possibly-self-inflicted 'rules'...
1. Subject may(?) have some aversion to EITHER man-made structures OR elevation
This is one that's been hinted at by M's rule of 'getting up high', and has been recently re-examined by The Gargoyle. Conventional man-made weapons have little-to-no effect on TPF, of course, but buildings seem to wear it down a bit. There's a possibility that TPF understands us and our structures as little as we understand TPF, and would be gawking at our structures as much as we would at the city of R'lyeh.
Oh no, did I just blow my cover on that one? Drat.
The other possibility is that TPF can't handle the fluctuating pressures caused by rapid gain in height or depth, and thus must slow down. Depends on if you've ever seen the Tall One climb a tree before.
2. Subject has an aversion to water
One of the few things that's been "proven" (using the term as loosely as is healthy) to work in warding off our mutual Tallish Friend is water. Kind of. Only moving, open water has been shown to have effect, and even then there's the fact that TPF has moved between continents freely. While it's interesting to contemplate TPF having a fear of drowning, perhaps something about proximity to the tides and currents keeps it away? Getting to that in a bit.*
3. Subject has a connection to forests and nature(?)
This one has never been really 'defined'. I've always assumed it was because TPF had the most opportunity to disappear in the forests, 'Slenderwalking' from the blindspots the trees provide, but perhaps there's something more to it. This needs to be looked into further... I say as if there's any feasible way to research this phenomena... but perhaps someone could try
4. Subject has some aversion to electricity
KK Collins, wherever she is now, was absolutely BRILLIANT in the procurement of this information. I'm not saying this one drives TPF off, no sir, TPF was absolutely LIVID about being shot by a bolt of lightning.* (A similarity to humans, perhaps?) But it may have stunned or even harmed TPF... if only temporarily.
5. Subject has been repelled by showtunes
Self-explanatory. KK again. It's difficult to tell if the positive energy of the music drives it away as KK said, if it's the erratic sound waves of the song that repel it,* or if TPF is just a really harsh critic.
Which actually explains a lot, but I'm getting farther away from the point.
6. Subject can be confused, or even have what could best be described as 'anxiety', under unusual circumstances
Do you really need to ask who I'm citing for this? Rest in peace, Mad Maduin, how I would have loved to meet you. Or at least ask if you'd be too disappointed I'm overusing your acronym.
7. Subject reacts negatively to mirrors (and cameras... ish)
Not that I advocate the use of the mirror,* but during the experiment I have just improperly cited, Kay found that the same noise TPF makes on camera is made against a mirror, so congratulations: your camera is just fine.
Although... the cameras capture the imagery/energy that Kay said the mirrors reflect, so maybe the camera eats the reaction for the Tall One. In which case your camera's absolutely screwed.
And may technically be haunted. And no priest can exorcise or bless it enough for you.
I'd like to say it's just because TPF hates HHIZ reflection more than an anorexic schoolgirl does, but given the lack of visible eyes, that's another one 'to be looked into'.
8. Subject has mixed reactions to "magic"
I get the feeling that if I were a practicing sorcerer or wizard or whatever that this would be a big steaming pile of basilisk dung spelled out into the letters D-U-H. Followed by a cloud of flies trying to form the letters V-A-G-U-E while swarming said feces. I apologize for not being clear enough to say what stones and herbs and symbols and foci actually work. I've read at least two reports of summoning/sending-type spells working quite effectively, and warding spells working inconsistently, but I really can't get any more specific beyond that.
There's enough practitioners out there that my speed-reading powers do me little good. That and since I have no idea how magic really functions- much to my annoyance and chagrin- I can't honestly define what does and doesn't work about it.
* Theory time!
Just to pull a few items with commonalities from out of the mix: Water, Electricity, Sound, Reflections/Light.
What if our mutual Tallish Friend has an aversion to anything that moves in a wave or current? I still don't know about things like the wind, but it's worth looking into, no?
I mean, yes, each of these items has their own way or reasoning behind repelling TPF, so expanding the field may be seen as a bit of a stretch. More individual testing would need to be completed by someone more capable than I, of course- Perhaps someone should try exposing The Construct to the activities of a church bell or one of those lamps used to kill bacteria, and observing the reactions?
Of course, don't be surprised- and be ready to run like the dickens- if it serves only to make TPF angry.
Has this terminology annoyed you yet? 'Cause I simply refuse to call the creature without any distinguishing sexual characteristics '
Anyway, this is everything I've heard works from my readings thus far. I've got a LOT of catching up to do though...