I had tried posting it on the official forums of rs, but seeing as OSRS Gold no-one responded, I thought I'd consider posting it on sals. My first idea is:Zombie Wars.
It's a mini-game for runescape , which allows you to travel into another world. Everything is normal except for a few things: everything is dark, deserted, there's a mist hanging around, the entire village are down and there are zombies all over the place.
It is believed that evil forces have driven guthix, saradomin (and any other gods who aren't in favor of zombies everywhere) from runescape. So now zamorak along with other gods and gods of evil have taken control, filling the entire world with zombies and skeletons and many other vile creatures. This minigame lets you only fight enemies, but not other players. To make it easier to work as the team, all locations are multi-combat.
Each game must have at least 40 players. Every player is taken to Buy RS Gold a city, whether varrock, lumbridge or seer's Village. The players must all defend their home until they've conquered all zombies they'll all appear in waves, with each wave getting more difficult. The final wave is wave 5, once they have overcome wave 5, they will be teleported by the spirit of dead warriors that died fighting zombies, to falador. There they'll meet with teams from other cities. All of them must defeat "the Hive" which is a huge gooey egg-like shape, it releases a horrible shot at the players, once they have defeated that, a giant boss zombie appears out of it. The game is at level 400 and increases 20 levels per player left on the field.