Awesome homework task!
I'm not too sure how you would approach this task unless I knew and/or were familiar with a *particular* gaming site, but I'll see how I go with analysing the mere bits and pieces I've observed here at ATARNotes.com

(using the examples you've mentioned just for ideas)
Formality:Many users type in quite casual responses. You can see this by examples such as 'can't' in lieu of 'cannot'; 'wanna' in place of 'want to', etc. This is an example of morphology, where you have shortenings and contractions, deemed more 'informal' discourse. Another example is of 'ellision':
ahh my mistake, ellision is when you get rid of a sound, but it works the same! taking the example of the sentence 'I saw this on .......' the user could type 'Saw this on...' and drop the unnecessary pronoun. This is also a syntax example, sometimes used to avoid repetition. The same can be used for 'Harry ate some cake and [ate some] pie too'.
Standard and non-standard:Pretty much ANYTHING. There are examples everywhere. People not spelling things correctly (which I probably haven't in this post!

), such as using the wrong 'practice' or 'affect'. Everything...
Some other subsystem features off the top of my head:Prosodic features used in written texts. I.e. when someone might write *inhales deeply* they're suggesting that they are taking in a deep breath, something that can't be physically written down as it is gauged as a phonological feature. So that's why we come up with written ways of expressing these things... *sigh* *giggles* *LOLLLLLLLL* etc..
Lexical choices..
Adverbials are sometimes used to shorten things. If you take 'at the moment' it becomes ATM. There will be PLENTY of specific jargon relevant to WHATEVER forum you choose to analyse. (Aha! Spelling "analyse" with a Z will make it non-standard, as it is American orthography!) But anyway, think of all the acronyms. Here, we have ATAR, VCE, VTAC, UMAT, etc.
Look at the syntax in terms of sentence structure and types.
You could make an observation that the first post of a thread tends to use interrogative sentences as they are looking for answers to questions. Generally the 2nd poster and subsequent ones will respond in declarative sentences to pass on information, facts, etc.
Also, those that are more elaborate in their answers *may* be more likely to use complex and compound sentence structures in their responses. You might be more likely to find those responses in specific subject threads such as English, or in threads where a detailed answer is required. Similarly, you might find more cliches, puns, metaphors, whatever in the threads that include those. Basically what I'm saying is, you might find more people using them in the English threads because those kiddos have them in their course content.
With gaming forums, those that might have a better online forum, thread, whatever reputation might be more likely to give more elaborate answers with complex sentence structure and ask less interrogative sentences than others due to their acquired knowledge about the specific jargon in the domain of COD or whatever.... (I am clueless, as I'm sure you've cotton on to by now

)
That's pretty much all I can think of at the moment. Hope that's of any help to your homework task
