For the first question, yes. I see no reason why you cannot bring NPC's into storylines, the main problem would be the handling of this. Since, obviously, you can't get an NPC to battle you on request (and I'm going to assume you don't have a mission for each NPC permenantly on standby in case you DO want to fight them) it would have to be handled "off screen" so to speak. The handling, again, is delicate. You'd need to ensure you could stay true to their character as well as that of your own and, more importantly, not do anything that really has an overt lasting effect on them. The other problem would be the "beyond mere rumours" part since, a lot of the time, it'll just be your word against theirs about what happened. If other PC's are involved in the story, and give consent, that's just more grounding as to the acceptance of the result. As long as it's handled delicately I see no problem.
For the second question, yes AND no. It really relates to the handling of the thing, as in the first question. Stating "I dropped Back Alley Brawler like a bad sack of manure in one punch. Now he hides from me constantly." Isn't going to cut it since he is, quite plainly, standing in the open in Galaxy and no matter how long you stand there he isn't going to run off screaming. That's an extreme example of bad handling (Not least because you would need to be a hero to stand in galaxy and beating on the Brawler isn't going to win you any awards on that front), but I'm always surprised the amount of people that will state things like that. On the other hand stating that you got into a fight with one of them but leaving it vague enough to be interpreted broadly is less of a problem in my eyes. So you got into a fight with Black Scorpion. You beat him. How? When? Maybe he was winded before hand, maybe you had help. Maybe he had the flu. Leave it obscure. Fill in what's needed but don't make it overly life-changing for the NPC involved.
For all we might wish it differently theirs is a static world compared to our dynamic one. Nothing can change them or their personality whatever you may write and should you attempt to I would wager more people will ignore that portion of the story than not.
If this sounds overly preachy or like a rant at your topic, it isn't (and I apologise if it does). This is just how I write.
Friends are just enemies that haven't betrayed you yet.
Well I like to do mission based roleplay. So if you do it in a mission then be free to brag a bit. But like you said don't overdo it.
Tricky one this, i wouldent play an NPC as high up as that or anyone in the Freedom Phalanx, but i would do an AV/Hero mission IC, for example Infernal is a classic, he pops up heaps of times Villian side. Its a grey area when he goes down, our excuse is that he uses the med-port button to get out of there similar to when my char gets KO'd. Then of course you get another mission with him in and you have to beat him, yet again he uses the med-port back to Paragon.
But if you do the mission IC, you come across Statesman for example and you beat him, well? You've beaten him and he's retreated back to Paragon. I personally wouldent include it in stories though, but thats just me i see nothing wrong with doing so though but! it matters what context in the story.
Some of the best IC missions ive done involved beating AV's. EVIL vs the Council, Requiem, Archon Burkholder, Maestro, Vandal, Nosferatu. All in one mission and it worked perfectly IC, and it was GREAT fun. We've also used Countess Crey in a few plots, or atleast one member has in Character plots.
Something I've been thinking on for a while, after plotting out more of my Rebirth story, that was highlighted in a discussion with Augury.
Namely, how much freedom do you think people should have with established NPCs in the gameworld? People like Statesman, Recluse, Requiem and so on - do you believe it's perfectly acceptable for your characters to get into fights with them? Do you feel it's alright for someone to have them saying and doing things beyond mere rumours?
While I'm asking this in the context of stories, it could also extend to Roleplay itself: do you feel justified in claiming the above things IC? Would your character tell another he's fought - and perhaps even destroyed - a member of the Freedom Phalanx?
Slightly rambling, but I figured I'd make something of a discussion out of it.