There are several piles or stacks on screen.
- Tap at the top to add something to a pile.
- Tap the pile itself to remove the bottom item.
- (Or tap a specific element to only remove that element, sliding those above it downward?)
The item could always be the same. Or there could be a “current item”, like with tetris.
Removing something might also have specific consequences. (That becomes the next item. Or special cubes have some “on_destroy” action?)
This might be orderly (in a neat, fixed grid), or physics-based.
Your goal is to make your stacks look the right way? Or to match 2 or 3 of the same color in a row? Hmm this is a very vague idea …