In my game, quicksand exists as a hazard where the player will sink and move slower, and begin taking damage after 20 seconds pass without getting out of the quicksand. Here are the 3 stages:
First stage: you move slightly slower and have 10 seconds to get out of the quicksand. When 10 seconds pass, you get to stage 2.
2nd stage: You move even more slower than stage 1 and have 10 seconds to get out of the quicksand. When 10 seconds pass, you get to stage 3.
3rd stage: You move slower than stage 2 and all characters continue to take 250 HP damage until they reach 0 HP or get out of the quicksand.
Here are two images, one showing the Events I set up and another showing the message when you start sinking in quicksand. I had to upload the images to my Sta.sh at DA since Quicksand Fans won't let me attach the images for some unknown reason.


If you want to see a short video of it in action, you can download and watch the video I made.