Check the post to which you're going to comment in- if it's a silly RP post, serious might look a little out of place. If it's serious RP, or serious OOC debate, silly RP might look very wrong ;) We only ask that you keep context in mind when posting. Apart from that, anything goes.
Multiple Matrix char's- we don't mind, but a good story for why you're another Trinity/Morpheus/Whoever is always worth it. Maybe Trin's code copied onto an AI, and you're that AI? Maybe you are THE Trinity? Same with others- give us some plausibility, and it's fair play. (Can be silly or serious- maybe you are a plot device, who knows?)
On Original Characters: While multiple Matrix char's aren't a big problem, stealing an original character- well, the muns (players) would certainly take offense to that, and rightfully so. It's their creation, while The Matrix is fairly public domain, as its creators get to make money off of it. Muns may not. Please don't come in as a duplicate 'Agent AndrAIa, or 'SigMaxIII/Pr0sthetic' or whomever.
(Mun notes that yes, she is indeed using a variant of Reboot's AndrAIa concept- which she has created something entirely her own from, and thusly, wouldn't like to see copied)
On Cliquishness: Don't bring it in here. If you have issues with something a newcomer suggests, or how they RP, take it up either privately so you can be blunt, or expect our 'politeness expectation' in here. We prefer to welcome newcomers and their characters, ideas, writing styles etc, and we only ask that everyone follow the guides- no ganging up on a new member for stepping over invisible boundaries created outside these and these alone! If we see that happening, case-by-case, action will be taken, whether its the 'gang' finding themselves restricted or whatever we deem appropriate.
Thus it was made so... Enjoy your stay in the Construct of the Free Minds!