How to train your T. rex:

She knew had to save them, but her opponent was too powerful.
Looks like a word is missing there.

Tensing her muscles, she leaped clear over her foe and sprinted after at them.
You need only one of these two words.

Open The Door, Get On The Floor:

The Stu and his brother about to head off to some kind of ComicCon.
Looks like a word is missing there

And while I’m on it, in Whitney and Backslash’s mission "Dundertale":

“* Oh yeah, you’re right! Backslash, is there any specific reason for the asterisk in front of the starting quote whenever we say anything?”
Isn’t the asterisk actually behind the starting quotation mark (but in front of what’s said)?

Whitney became aware at that moment that they hadn't bought any Tem-Flakes with them ...
I guess you meant "brought".

HG

Glad to see that I put this fic into good hands!

1) Cupid looked like he was about to protest, but wisely kept his mouth shut when Sarah sent the pair one of her “Shut-up-now” looks.

First of all, please lowercase the S in "shut-up-now". Also, either remove the quotes or the hyphens:

one of her shut-up-now looks
or
one of her "shut up now" looks

2) I shouldn’t have sent my message to the DF! I should’ve known he was there!

As written, it sounds like Sarah did not know that Ripper was in the DF, but should have. I suggest replacing "known" with "remembered," or "should've known" with "knew":

I should’ve remembered he was there!
or
I knew that he was there!

3) Anyway, a translation spell?! Celestia actually has one? And she uses it to make the raptors talk?!
What's with the outrage? I've seen translation spells appear in goodfic, most notably in an XCOM/FiM crossover called "Stardust". It may be non-canon, but I don't get why Sarah is getting apoplectic over it.

4) You have to consider the raptors, and that weird watch thing that he’s got!
What weird watch thing? Do you mean the gauntlet that he bought at the con? Please make the connection clearer.

5) Cupid looked livid. “Okay, I don’t know either continua here, and even I know this is gonna be bad!”

Number agreement error. It should be either "either continuum" or "either of the continua".

6) exhibiting terrible beige prose and questionable grammar; having no qualms about using your stolen ‘pets’ to kill stuff; attempting to kill Discord; and a metric buck-ton of other charges I don’t care about right now! Can we portal this bucker to the Yucatan? There’s a meteorite out there with his name on it!”

Sarah is obviously talking to her fellow Agents at "Can we portal." That needs to be a new paragraph.

7) Sarah gave Suta a pitiful look, but she flashed a sympathetic smile and waved at her, before following Tianlong out of the ward.

There's a grammar error. Here is how I understood the sentence as I read it:
Sarah gave Suta a pitiful look, but she [Sarah] flashed a sympathetic smile and waved at her [Suta], before following Tianlong out of the ward. [Wait a sec: Sarah followed Tianlong out? That first "she" must be referring to Suta! Grammar error.]

Since Sarah was the subject of the sentence, once I saw "she," I understood it to mean "Sarah," the subject of the sentence (especially since we have two females in the sentence). Use the names instead of pronouns.

8) Was it because I hurt you family
That should be "your family".