Much better. Still, I found a few things that I'll point out, but it's getting there.
Turtwig, dodge it and use solar beam" cried Marcus who was feeling worried for his Turtwig.
"Turtwig, use synthesis" muttered Marcus who began to feel a lot more nervous than before.
Okay. This kid has only two badges, you said, right? He'd have to have trained
a lot between those two badges for his small, unevolved Turtwig to pull off a powerful Solar Beam attack, or the experienced healing skill of Synthesis. Levels normally don't exist in fanfiction, but their concept serves as a guideline. So, if Marcus only recently obtained his Turtwig, and has only gotten so far as to obtain two badges with it, it seems only reasonable that unless he went through some sort of specific move-training efforts to develop these two moves specially and before the Turtwig should be experienced enough to grasp their concepts normally, his Turtwig should not be capable of using Solarbeam and/or Synthesis. If it were skilled enough to use those moves, then it would most likely also have lost much use for the move "Tackle" because it would have memorized stronger but similar moves such as a simple Headbutt or Take Down (though it doesn't learn those moves technically, they are simple enough for practically any Pokemon to be capable of using them).
Darius looked at Turtwig with evil eyes, he wanted that Turtwig out.
Darius looked at Turtwig with evil eyes. He wanted that Turtwig out.
^Make proper use of the period. For the proper feel, it works much better and is much more gramatically correct than a comma.
Also, you seem to use "Turtwig" too much. Here's a couple examples of how this can be replaced for the same meaning and effect, rewriting parts from the chapter:
"Turtwig, dodge it and use solar beam" cried Marcus who was feeling worried for his Pokemon.
"Turtwig, use synthesis" muttered Marcus who began to feel a lot more nervous than before. The turtle-like creature responded with a sparkle as it began to recover. Darius looked at his foe's Pokemon with evil eyes. He wanted that Turtwig out.
See the effect? Saying "
Turtwig responded with a sparkle as
Turtwig began to recover" is not just repetitive, but it confuses the reader, because normally the only reason you'd give a name twice in this way would be to show two different characters, such as if Dragonite had been told to recover and Turtwig was responding to its trainer with a sparkle. In any work of writing, pronouns such as "it", "he", "the -whatever it is you're talking about-", and the like are very important to be aware of.