Alright I am putting this here, using the magical powers of the internets.
PvP
This is my idea for the basic PvP Arena. It's pretty simple.
Instead of going in with set equipment, you can only use one weapon at a time. You can't switch weapons like normal, you have to pick up one of three power-ups.
Gun, Sword or Bomb.
If you have four swords or four guns, it will randomly pick one of the four weapons you have equipped.
If you don't have a weapon of the item you're trying to pick up, it won't pick it up.
Shields are also a power-up. You have to get use of them by picking up the shield power-up. Your shield doesn't regenerate in PvP, instead it deteriorates and breaks until you pick up another shield power-up.
You can pick up and throw other players, using them as projectiles. You can also throw fainted players and fling them around as well.
Throwing deals some damage, but it's mainly for getting enemies away from you or sending teammates into areas higher up.
Some arenas might have holes in them or have no walls around the outside, letting you fling them out of the ring.
This would really only work if action and attack were different buttons though.
Vials, hearts and other throwable items will appear around the map.
Lucky Boxes also appear around the map, you can pick them up and throw them or break them where they are. They contain a diverse selection of power-ups or power-downs, you can get temporary invincibility or you can get a super-stun and not be able to move.
Lucky Boxes only appear later on in battles to bring them to a close faster.
Mechanics
The mechanics of PvP are very much the same as in PvE.
If a team-mate is downed, you can sacrifice half of your health to revive them.
A player who is downed loses all power-ups and their weapon.
A fainted player can view other players playing, if it's in a team based mode they can only view other team-mates playing.
Maps consist of small, medium and large types.
Small maps are for 2~4 players, medium is for 4~8 and large is for 6~12.
Last player/team standing wins and starts the next round with whatever map they want.
The player/team who came last can choose what weapon they start with in the next round.
I haven't really bothered thinking up rewards, or maps.
But if they're that important I will post some here.
I think this sounds like a very fun idea. The one problem I see is your weapon selection, but maybe I'm just not reading it correctly. Based on how I understand it, the weapons are chosen based on what a player has equipped before entering PvP, which means that I'm going to unequip everything except my Cryotech Alchemer MK II and then be guaranteed it. If it's based off what you have, then that really sucks for those players who have been stocking up on Brandishes to supply newer players, as well as those who have tried experimenting with bombs and have a few, because it will drastically reduce the chances of them using a viable weapon in PvP. Am I understanding this correctly or did I miss something?