Basically, this would be a standard type marathon of a game series, but with one major twist: The player/players must play the game in a way dictated by the donators. For example, if there was a Halo marathon (which I would totally be up for participating in), the donators would have the option of imposing special conditions, like the players can only use the plasma pistol, can only use melee, must not kill any enemies except when required, activate skulls, up the difficulty, can't use vehicles, etc.
I know something like this has been used a little bit in past marathons, but this would be ALL the time. Either:
1. the schedule is seperated into 15/30 minutes segments, and the donators donate for a specific challange for a specific time. Special conditions that are based on a specific part of a level, like a boss, would just be used whenever the player reached it.
2. Every donation challenge is activated immediately for 10/15 minutes, and they can stack, meaning the donators can REALLY mess with the players. Challenges for specific parts would be activated whenever the player reached it.[/spoiler:3icj0f1n]