Greetings! I couldn't find a better subforum for this thread.

The thing is, I am suddenly and irrevocably sure that with current Torishop items sale a mistake was made.

What a great post

Massive discounts left right n Centre

On a serious note, this is most likely not an error; discount section of the Torishop has been used more as an "offers" section as well, with the usage in this instance showing that, just as written in their descriptions, items that are HALLOWEEN SPECIAL are in stock - in other words, they are there to show availability; see how the Hunter & Mayan prices are discounted properly?
Reason behind the crossed pricing? well, this whole description idea was implemented much after Torishop discounts became a thing. Example.

AFAIK there are items for events similar to this that are usually not available for purchase until the event arrives. Notice how there are no Christmas-themed items under the 3D Items section either? Same thing goes for them; they have CHRISTMAS SPECIAL as well. Example.

Edit: forgot to mention that some newly released items might be under discounts to celebrate its release. Sometimes they are actually discounted and other times not.

At least this is what I can make out from this, please correct me if I'm wrong.

Well, that's a point to which I agree. Using the sales utility to show the availability of seasonal items is a good way to catch the attention of players who might be interested in buying those.

However, there is one certain item, 'Brain', and the price for it was lowered from 3 ST to 4 ST. This is at least funny if not ridiculous.

Nokia is right, sale section is sometimes used to promote seasonal items - this is currently the case with Halloween stuff.
"Brain" item has been on an actual sale last weekend, some other items will go on sale in the weeks to come too.