In movies or on TV usually for entertainment reasons, quicksand is quite often and inaccurately portrayed as a kind of super fast acting, almost inescapable and extremely deadly trap capable of swallowing entire humans and animals whole.
So in my world there's this weird grenade-sized projectile that essentially does this very same thing. Upon activating it causes the ground underneath its victims feet and within a certain radius to turn into a strange sticky tar-pit like substance (basically fast acting quicksand but much harder to get out of, which is why I've decided on making it sticky substance instead)
This causes victims to rapidly sink inside the ground until the chemical reaction or strange phenomenon eventually ceases, re-solidifying the ground underneath. Which either leaves the victims trapped or in the worst case scenario encased/swallowed whole into the ground.
I've was already planning on handwaving this with magic but I ask this question more-so out of curiosity that anything.