Would not have gotten at all that the death glare from Admin-chan meant that she was the mole without the note at the side (is there a word for that?). Not sure whether to consider that a failing of the manga, a failing of my own, or the editor overstepping a bit on the note.
Was Riko introduced before last chapter? Is that what the extra page is saying? Or was that the introduction it's talking about?
Well because I think it's wrongly translated?
My Japanese is not the best...I think the first sentence it kinda says "Is the admin (secretary) the mastermind?" (of that bully group) The two chapters before they mentioned a mastermind behind the bully group!!!
Maybe translator mixed things with mastermind and "inside man" but I know they use sometimes the same Kanjis for it because sometimes the inside man is the mastermind of all the plot?!
The second sentence is right!

This is the word in question, literally "black curtain", it's a term originating in kabuki I believe. A wordier definition would be "Those who do not appear on the surface, who instruct and make a measure. behind the political world."
While "mastermind" is a valid translation, I'm being a little reserved in using something that would imply little Riko has a leadership role in whatever criminal organisation is shaping up. Koinami refers to a "queen" she is working for in a previous chapter, I translated as "her majesty" for the sake of clarity, but when we've seen this character in silhouette they clearly have braids, which Riko does not appear to. Additionally, Niina had no special reaction to Riko until the end, despite worrying about her failure becoming troublesome for Her Majesty.
A more direct translation that doesn't imply leadership necessarily is "fixer", but I shied away from that one as well because it's still entirely possible that Riko could do a hairflip to reveal her braids, and suddenly it turns out she's been Her Majesty the whole time. I've already had to pull off some fancy footwork with the whole detective arc in order to make previous translations and the big turnabout scene feel congruent, I didn't want to get myself into a situation where I had wrongly implied Riko was merely another lackey.
Hence, "inside man". we'd suspected there was someone inside the student council and Itsumi's proof left a clear opening for it, Niina got the code from someone else, and here at last we see who was inside the student council the whole time.
Is it just me, or is the amount of text increasing with every chapter?
Yes (._.;;) Appreciating now the reason I was able to fly through translating the dodgeball chapters is that there's not too much talking in an action sequence.