The Rival Challenge (previously 30 minute challenge)
This is something I invented a while ago, but that did not end up seeing the light of the day until a kind soul in #oi agreed to do it with me. His name is Deino and currently he is 2-0 against me, which is obviously intentional because winning keeps people playing.
The 30-minute challenge turns every participant into rivals that meet each other to battle at unexpected times during the in-game campaign. It is based on the stories I've read about people buying Pokemon games together and agreeing to play through and battle each other after every gym or something.
You need the following:
1. Two or more participants. I'll assume two for now because it makes explaining everything easier. They need to be in touch with each other, easiest way is obviously IRC.
2. All people involved need working copies of the same game or equivalent games (say, Ruby and Sapphire is fine), a working online battle simulator such as Pokemon Online (make sure everyone uses the same one) installed, as well as too much spare time on their hands.
3. Some way to keep track of time, preferably an alarm of some sorts.
After a countdown, a timer is set for 30 minutes and the players start playing their games. They will be playing the game for 30 minutes, free to do whatever they wish during this time. When the 30 minutes are over, everyone has to stop playing. A rival encounter happens now, and both players will start inputting six of their current Pokemon in a simulator. Since mimicing the exact in-game teams fairly is tedious, the following rules apply:
1. Species, moveset, level and nature must be the same.
2. All EVs are set to zero, unless something else has been agreed on (such as a total EV cap for each team or each Pokemon).
3. IVs are all maximized (15 for RBY and GSC, 31 for later games).
4. No hold items, unless something else has been agreed on (such as each Pokemon being allowed to hold any item currently obtainable).
During battle, the only clause to be checked is Sleep Clause.
What you end up with is an entertaining sort of speedrun/race through the game where each of you tries to counter the other person's team the best they can. I've found it a lot of fun so far. Some experimenting with different rulesets may be a good idea. 30 minutes seems like a good time frame so far, but you can try 15 or 45 or 60 or whatever floats your boat.
One thing that does need attention is the starters. The run I'm currently playing against Deino, I made sure we both picked the same starter, since otherwise one person would have a huge advantage over the other. I think some additional ruling regarding starters may be required, possibly banning them from the online battle. It's very easy to semi-solo the game with the starter and destroy everything the other person has tried to train, or even if there's some good counters available the game gets centralized around them a little too much. So if any of you tries this, consider banning starters altogether, or applying some kind of rule where all Pokemon on the team must be within similar level range or something.
For more than 2 players, the online battles should be either round robin or some kind of quick single elimination tournament. The more the merrier! But I can't imagine more than 2 people being able to stay online together for very long.