Hi! So, there are no co-op runs of this game available, as there isn't really a way to integrate them properly. There are individual levels that can be co-op'd, but not the main story. We've had people ask about it in the past, and there's no real way to comfortably do it and have it be something that can be verified. Even aside from the book keeping headache, it's ripe for abuse.
This particular board is mostly for solo Real Time Attacks of Ceadeus and Ivory Lagiacrus. Cha-Cha% is something of a joke category just to have something short, and if anyone can do Alatreon in one sitting...Not sure that one's going to happen. Any items or weapons are fine so long as you get them during your run itself, an exception made for the DLC items you can get for free.
Something the other mods and I were big on when we formed the rules is that we're not going to restrict what tactics are available. That's popular in individual hunt speedruns, but not so much RTA. You can submit runs to the categories here and I'll honestly be happy to see someone else giving it a try, but it sounds like you and your friend might be better off just dicking around and uploading to youtube. :)
I have just uploaded a new guide for the speedrun, focusing on the monsters and their attacks/behavior in Ceadeus%. It is mostly for newer players, but those who are having a bit of trouble it might help.
Firstly, I'd like to congratulate you on your Cha-Cha% WR! I have yet to watch the VOD for it, but I look forward to doing it. It's the one category I haven't run (no one is ever going to run Alatreon, not even me) and it'll be interesting seeing how you do it.
Regarding your question...It is not in the rules because it seems pretty obvious. Very few speedruns involve multiplayer of ANY kind, and those that do are clearly marked. Our Individual Levels categories, for instance, allow you to submit times for 1-4 players. I look forward to filling some of those out in the near future, in fact.
However, for single player runs, it is simply out of the question to have other players enter the picture at all. It defeats the point. The goal of this speedrun is to complete the one player campaign (or sections of it, at least) as quickly as possibly on your own. I appreciate your looking for ways to exploit the run and cut that time down as much as possible, but it falls down to us mods to consider the SPIRIT of the run as well as the letter of the rules. This is a long run, but it's based almost entirely off of knowledge of the game and skill at executing each and every fight.
And frankly, because of this we'll be more specific and state that there are no other players allowed. It's one thing to pop into the marina of the offline tavern in order to buy rare goods from Granny. It's quite another to sit around while some HR 999 friends spend roughly an hour getting you to HR so you can cheese getting a better weapon and some basic HR armor to chew through the quests in 3 hours.
This makes 3/3 of the mods for this game voting against your idea. I'm sorry to shoot you down, man. If you can think of any other potential avenues to exploit things or cut down the time, let us know. We ARE open to optimizing this game as much as possible, so long as it's done fairly and with the spirit of the run in mind. And I look forward to seeing you submit times for Ceadus and Ivory runs!
It's been the topic of debate for quite a while now. I've seen a lot of arguments about it. On top of letting people do both as they want it, it might stop some of the really dumb fights I've seen it. Split em.