Everyone likes to play bad games. There are games that are deeply flawed, but amazing because of it. These games are fun to play, just for the sheer spectacle of how bad they are.
Your target is to make a game that is 'So bad it's good'. The type of game which is by no means 'good', 'well-made' or 'polished'. The game has to be entertaining.
Oh, and you have a week to do it.
This does sound weird, but what's the point in making a game which is boring? It can't be mundane, it can't be mediocre. It has to be so bad that it entertains you.
However, if you want to base it off an existing IP, please do it in the style of a knock-off. Don't use assets you are not allowed to use, and think of a funny name, like "The legend of Zanda" or "PokeCreatures". Doing this will probably benefit your game anyway.
Go nuts: make the game how you want it. Just make it bad.... and good.
The jam will be voted on, and the 5 best games will be bundled into "Best of the Worst" bundle. In this, the best worst games will be available to download as a single file, as the end product of the jam. The No. 1 winner can choose whether the bundle is free or paid, and if so, what charity the proceeds will be sent to.
Good Luck, and have fun!