I thought that your introduction was pretty good. It drew me into the story so that I could find out the identity of this mysterious attacker, and it was described with enough detail to allow me to see what was going on. I specifically enjoyed how you continued to build the suspense and danger of the scene as the introduction went on.
Josh wiped the rain droplets from his glasses as a brown blob emerged from the mud. Where one would expect its nose to be, the brown became pink. Soon after, another one appeared right next to the first, before being followed by ten more. Unless Damien has evolved into a rather numerous Dugtrio, the sixteen-year old brunette thought, he’s still in the mud.
Good job with this section.
Having been ambushed by a Shellos, Josh attempts to escape with Damien in tow (who has fainted). The Shellos wants revenge for an event eight years before the story, which is shown in a flashback. Despite the elements working against him, Josh manages to get to the Pokemon Center in Floarama Town intact.
Scaled down to its basic components, this plot is quite simple. I don't really think that's a problem, since your details of the situation and your ability to build the suspense throughout the story kind of carried the story as a whole, and your target really doesn't require anything all that complex for a plot.
As always, future, more difficult captures will require some more complex plots, but for now, I think this is fine.
None! It makes sense, since Josh is the only English-speaking character that takes on a main role in the story. However, I felt that a little dialogue placed in the flashback scene would have livened it up a bit from what it is now (it's more of a brief recounting of previous events as-is than an event that someone would recall when their life was in danger). It's not too big of a problem, since you're going for something simple here, but in the future, you may want to give more dialogue in the flashbacks. Though in most cases, the actual spoken words of a situation escape our memories, more important points in our lives often leave vivid imprints on our memory, so including dialogue in the flashback would have been practical as well as helpful.
However, given your target, it's not really a necessary thing.
When you write out thoughts, even if no other characters have spoken or thought anything in the paragraph that you're writing them, you should still give the thoughts a new paragraph to separate the transition from description to dialogue/thoughts. For example, this:
Would become this:
He could run maybe nine kilometres an hour, and the nearest Pokecentre was in Floaroma town – about three kilometres away. It would take twenty minutes if he could keep with this speed, but he had been body slammed in the ribs and his feet were covered in sloshing mud. It would be a hard trek, and an angry Shellos was chasing him, but he needed to do it. For Damien, he thought. I have to get there.
This is a bit of nitpicking, but at times, it seems that you're missing some "t"s:
He could run maybe nine kilometres an hour, and the nearest Pokecentre was in Floaroma town – about three kilometres away. It would take twenty minutes if he could keep with this speed, but he had been body slammed in the ribs and his feet were covered in sloshing mud. It would be a hard trek, and an angry Shellos was chasing him, but he needed to do it.
For Damien, he thought. I have to get there.
This is simply a case where better proofreading will be useful, so try to read your work carefully in order to pinpoint these small errors. You wouldn't want them accumulating on you, after all!
but he strength of the impact added to the deep mud impeded his movement.
and began fishing in he mud for his friend.
Other than those couple of errors, I really didn't find anything of note.
Detail and Description:
I thought that, for the most part, you did a good job in this section. Your description of the environments that the story took place in allowed me to visualize the scene, and the fleeting details about Josh's outfit that came bit by bit as the story went on allowed me to visualize him in the situations that he was in.
There were a couple of things that I didn't like about your details, though. For one thing, your description of the Shellos emerging from the mud kind of messed me up:
I wasn't really certain what part of the Shellos' anatomy you were referring to here; Shellos' flower-like appendages on its head (West form) only has six tendrils, so in my first read-through, I actually thought there were two Shellos. Further clarification on this would be handy.
Where one would expect its nose to be, the brown became pink. Soon after, another one appeared right next to the first, before being followed by ten more.
Before he managed to begin searching, however, the eleven Diglett-shaped brown blobs slammed into him with its entire amorphous shell body.
While I liked the story overall, I have to say that it messed with my willing suspension of disbelief a lot with certain details. For the most part, this story depicted Shellos as a mud slug, when in actuality, it's a sea slug, and thus, probably wouldn't be beached in a huge depression of mud. And speaking of which, why was there so much mud on Route 205? The only route in Sinnoh that gets as much mud as you made it seem there was in this story is Route 212, and, as you'll notice, Shellos is only found on that route in Platinum.
However, this is also kind of nitpicking, so I'll be moving on now.
As I said in your last story that I Graded, further involvement of Josh in the battles was needed. It made more sense this time why he couldn't be involved, but in the future, you'll definitely want him to be involved.
Also, I recall from your previous story that you made it ambiguous what the Diglett were using to Scratch each other with. Your description of Sucker Punch lacked that subtlety, stating outright that Damien has some sort of arm with which to punch the Shellos. It's not a big deal, but you'll want to keep constant whether or not you're giving your Diglett arms. Since they are moles, and all, it wouldn't be a bother to mention that they have short, stubby arms with claws on them, or something to that effect.
Besides that, I thought that the battle was done well. The attacks and their effects were explored adequately; in particular, I like how you explored the environmental effects that Earth Power would have had. It brings me to wonder if, since it was a strong attack, it messed with Josh's hold on the cliff face or not. But that isn't a necessary detail; it's just something I thought of as I typed this up.
Shellos is in the Simple category; the suggested length for Pokemon in this category is 5,000 to 10,000 characters. Your story is 8,328 characters, so it makes the cut.
Drum roll, please...
Gotcha! Shellos was caught!
No fancy ending this time, since I can't think how I'd get that Shellos into your party without having it attack you again. Yay for laziness! xD
Enjoy your catch!