I modeled it after Minesweeper. But I used Scrabble tiles. I gave different players different levels of information about the rules of the minesweeper game (the Warforged got a card that said "on your turn, choose a direction, flip over the tile in that direction, and move the token onto it" while the Kalashtar got "This is a game of minesweeper. Vowels are zeroes, other letters' scores signify how many mines are adjacent. Anything with a 4 on it is beneficial to the party, while mines are detrimental. If you step on a zero, you may reveal up to four adjacent tiles.")
In a fit of quickness last night, I even wrote a program to help me set up the map of the board... I knew I had seven potential "mine" tiles (mines were K, J, X, Q, Z, and the two blanks), and was most restricted on "2" tiles (seven of those... though when I looked earlier I thought I only had six). So I had to be careful about the placement. In about an hour and a half I whipped up a quick little Java Program (requires Java 5, I think) to let me lay out the board and count up tiles.
Can you tell I'm impressed with myself? Or even surprised at myself?
Mmm... energy, and creativity. for once.
During the game itself we managed to wrap the mechanic in enough roleplay to really make the thing come together well. Only a couple glitches came up - one as I realized that I'd put two 4-point tiles next to each other (a W, marking a spot with 4 adjacent mines, and a Y, which is sometimes a vowel ;-) and didn't have time to set up the next "positive" reveal before they could pull it off... and the other as I realized that I hadn't really decided on an end condition for the game. I decided that 1) the Judge was getting convinced, and wanted to get on with it, and 2) had the ability to teleport the conversation marker at will. I didn't really come up with a good way for the players to discover where the "Y"s were; that would be an improvement in the future.
But really, a key attribute of this mechanic was that it was new to the players, used something familiar, but exercised their brain in figuring out the implications of this new weird system... By the end they had it pretty well worked out, and a second game using the same mechanic would be pretty straightforward, I believe.