Stack Smash is a descent game: a tower of rotating platform rings, and a ball that smashes down through them — except for the black segments, which end the run instantly.
The rings rotate, so a safe gap becomes a black segment while you're waiting. It's a timing game with a satisfying amount of destruction attached.
Landing on a black segment. The rings rotate, so a gap that's safe now may not be by the time you drop.
In most versions, smashing several rings in a row builds momentum that lets you power through black segments — which is what makes long chains worth attempting.
Yes — tap or hold. Nothing to install.