Quicksand is a hole, which will drag players into itself if they stand too close to it. If a player doesn't manage to escape and falls into the quicksand, they will instantly die.
The quicksand is dangerous, although it can be useful for easily defeating enemies. Try to knock down an enemy standing near the quicksand. The Kick and the Roll are great moves for knocking down enemy players.
Avoiding the Quicksand
The best way to get away from the quicksand is to sprint while jumping. When you jump, you won't get dragged towards the quicksand. It is also possible to continually jump while over the quicksand, even at the centre. This prevents you from being sucked in. Somehow.