what!?! I guess the Gang is bored of adventuring so they try out warfare(probably fighting against the Yellowbellies

)
Seriously, that made my day so far

Their poses are so funny... and their 'jobs' are well-choosen

Let's start with Ruby respectively 'The Fast Runner Infantry'(the title alone is quite funny

):
She looks great, the lineart is really good and her accesoires and her weapons look ever greater

they're drawn with love to the detail

Another positive point is you made them pretty colorful and stained.
now Ducky the Parade Swimmer : beware, she'll slice you

Well done! nothing to critizise

Though she's a bit blurry.. but I assume it was on purpose to show how fast she is on her little legs?
The colouring is awesome, I like how you used this more dark green to frame the light green parts : yes Have you used a different coloured pencil for this? Might be something I should try with my fanart

Again the accesoires are very detailed.. the sword is awesome ^^
Now Cera, the Threehorn Medic, she'll bring you in safety, no matter whether alive or dead!
Her face..

she looks pretty good as well ( I see you used these frames for every character)
just a little thing: I'd say her legs are a little bit too thin...
Oh well, Petrie the Flyer Pilot: he'll bring you whereever you want, quick and safe
hehe, I somehow laughed the most seeing Petrie... this thing that I take for a device helping him to breath in big heights looks kinda funny
He looks good.. nothing more that comes to my mind.
Chomper, the Sharptooth Sniper: He never misses his target(and he has his victims for dinner btw)
oh, vonboy will like that one

Nothing to critizise, it's AWESOME!!!
next one: Spike, the Spiketail Gunner: hard to get down
Despite his head might be a little bit too big he's awesome, too. I like his expression: chillaxed, cold and angry at the same time

His gun looks nice ^^
And last but not least Littlefoot, the Longneck Captain: LONGNECK RULEZ!!!
I know this face too well.. I see it everytime I'm here

seriously, I mainly use screenshots, too
It's kinda hard to get the right colour of Littlefoot since it's not a common colour for coloured pencils... I usually use brown because it's easy. His actual colour is a form of purple, but I personally prefer brown. His colour changes from movie to movie, slightly though. On top of that you could confuse him with Ali(especially from the TV Series, where she has exactly that colour you used.
Anyway, except the colouring, which isn't very good imo, I really like him. The lineart here is pretty good.
End of the sermon
To sum up this I can strongly recomment you to do more fanart. You're talented man!!!
(I think it would be funny to think of captions of this

though I don't think fanart is allowed there :/)