Obu? Didn't expect to be called here. But alright, I guess I have a bunch of questions to try for...
1. While I may be a new arena fighter, if we were to have character who "survive" their battles, could they potentially learn from such an experience? Like say if my heavily armored fighter figures out some flaws within his techniques and tactics after they've been exploited by another, could I justify having him learn how to cover those weaknesses before the next fight?
2. What are the limitations of items used for combat? Obviously an armor made of an unbreakable material is grounds for an overpowered character, but regular steel full plate does happen to do a pretty good job at keeping pointy blades out of your fleshy bits. And what about those who have magical armor or simply one of high quality? A similar deal with weapons too. As silly as it may sound, I do kinda envision a future where my brawny heavy armor fighter goes up against a modern soldier and having a good chance to deflecting/shrugging off the bullets with his armor.
3. Reasonable amount of skills/proficiencies for low level characters? My character is basically an Arena adapted version of my level 6 pathfinder orc fighter, but inventory aside, his feats and skills at least mean he's proficient in all simple and martial weapons (That's everything from clubs to spears to bows and crossbows, various swords, axes, clubs, and polearms), as well as one exotic weapon known as the double orc axe. He also has feats for two-weapon fighting (which allows him to make use of that double orc axe), toughness, and the ability to channel all his might into a single focused blow (Power attack + Furious Focus). I also had it in mind for my character to take feats to make him more proficient in heavy armor. That is to say, the usual "Weaknesses" like being slow and cumbersome becomes mitigated as he drops the armor check penalty to zero (Currently for my character it's at a -2, which is a big improvement over the usual -6 from full plate).
4. Are we limited sticky to human/humanoid fighters? Amongst one concept I have is an amorphous character who is akin to Arakune from the blazblue series, but giving up his Curse ability for greater defensive ability and agility. Not quite a stonewall in the sense he's nothing but defense, but neither is he a fragile speedster in that he can't take a hit, but fast and durable at the price of lowering his overall damage output. Also the fact he's a shapeless, amorphous being. Can't exactly grab his nonexistent arm or decapitate his nonresistant neck.
5. This one is more character dependent, but if our characters have a penchant for "Cheating" or "Dirty Fighting", do we need to inform our opponents if we chose to express that by bringing allies? Like if I create a fairly roguish character who runs with a gang, and calls on that gang to swarm my opponent while he gets a stab in between the bodies. And I don't just mean my own NPC's either: I'm wondering if I could even call in another Arena fighter if it's within my character's personality.
Learning from a battle is perfectly fine, as far as i know. That's why people often test their characters in practice matches.
Regarding questions 2 and 5 - all is fair as long as it matches your opponent's strength. Three foot thick ceramic armor that can keep you safe and sound under a tank barrage? No prob, as long as your opponent has a fair chance against it. If summoning additional characters to the field doesn't give you an unfair advantage then it's fine as well. But if it's literaly cheating, you'd need some good luck to find someone brave enough to take the challenge. Not that there aren't such people, but most arena folk prefer a fair and even fight.
A character's skill with a weapon is often just fluff in the arena, as what determines it is actually the fighter's own knowledge: saying that your character is a master swordsman doesn't mean you'll be able to have them fight as good as you imply. Things like rope walking or driving vehicles is fine though, as those aren't central to combat. If we were hosting a textual rope walking competition, where we would be comparing one's knowledge of rope walking techniques, then this skill would be more relevant, but (thankfully) this is the arena.
Having characters be capable in a wide sphere of such 'miscellaneous' skills can indeed up their power level, but it'll probably be quite obvious when that border is crossed.
And finally, no, the variety of forms your character can take on is limitless. Humanoids are just close enough to us, humans, to use real-life combat techniques, making fights a bit more interesting, but you're welcome to try anything else.
