Upstack refers to the pieces dropped onto the playfield. Upstacking refers to "stacking up" pieces to score larger line clears, usually on the bottommost rows of the stack. Note: I have ignored holding and soft dropping for this article. Their use can make some ideas difficult to explain. Aim to keep the stack open to multiple placement choices, since you won't always get the right piece. When pieces don't fit, you have to create holes and gaps. When you can't clear lines because of the holes, you must stack even higher. This ultimately leads to topping out. Build so that there is a good spot for any piece. Even better, build surfaces that will also maintain goods spots for any piece after receiving any piece. Good and bad surfaces The left surface below has no place for S-, Z-, T-, and O-pieces. The middle has no place for O-, L-, or J-pieces. The right has no place for S- and Z- places. By having bumps and flat areas, you can accommodate all pieces. The O-p