Oh, poo. I thought I got all of those. (nm)

There it was, hanging on one of hooks on the entryway wall.
Missing word "the".

Part of the problems I have with the following may come from me not knowing Ajax’s home continuum. Apparently there are magical letters Ajax can use to cast spells. Anyway, after While there wasn’t any clue on the envelope to discern which letter it was, I would expect some clue elsewhere. I certainly wouldn’t expect the sentence to be continued with but. What is this "but" meant to contradict to? Is the envelope was black with some red edging on the flap thing a clue that this can’t be a magical letter? Maybe you just need to omit the "but", but I really don’t know whether I understand what you are trying to say here.

It didn’t seem to damage to the note inside though.
These are either too few or too many words. If "damage" is used as a verb, it should simply read "seem to damage the note"; if "damage" is used as a noun, it should read "seem to do damage to the note".

(thought it was a small step up from the one Techno-Dann used, it actually had a readout)
You probably meant "though".

Unlike their RAs, Matthew’s and Ajax’s Combined Content Analysis Devices were both newer, smartphone-shaped models.
This is a bit confusing, because you previously said that Ajax’s RA resembled a generic smartphone. Thinking about it, I get that the point here is "both" (Matthew’s RA is an older model), but I wonder whether this might have been made clearer.

What would have shown data on a character were currently displaying the following:
Are there at least two "things" that would have shown data on a character? Otherwise, the plural "were" should be a singular "was".

A bunch crystalline-like shards of light surrounded Matthew ...
Missing word "of" after "bunch".

HG