my favorite from this thread is chris's start at 30 and countdown.
"Start with a counter that you set to 30 (the average number of pulls in a Jenga game - but you could set this to anything you like). When you're instructed to pull from the tower, reduce the counter by 1 and roll a d6. If you roll equal to or higher than the counter number, the tower falls."
but my husband suggested rolling a d12 instead, for a chance of the tower falling after 18 pulls rather than 24.
i have the following paragraph in my game, which others can feel free to use also!
"If you don't have a jenga tower, you can play without one or use a dice mechanic to simulate the degrading nature of a jenga tower. Set aside a number of dice with their displayed values equaling 30, such as three 10-sided dice or two d20s with one die turned to 20 and one turned to 10. You will not need to roll these, but will use them to count down from 30 to 1. Each time you would pull from the jenga tower, reduce the number by 1. When you reach 12, each time this number is reduced, roll a 12-sided die (or two d6s). If the number rolled is equal to or higher than the number on your count-down dice, the tower falls."