MKO Stacking

MKO Stacking (Japanese MKO積み) is a way to stack the first bag which can be continued with T-Spin Doubles and/or a Perfect clear.

First Bag
The opener needs L and J piece relatively early in first bag. L and J are placed flatside down 1 column away from each other. Then, S and Z are dropped vertically on them. The T-Piece is kept on hold.

4-lines Perfect Clear
There's a 33.3% chance to get a Perfect clear after dropping 10 pieces. The O piece must come early in second bag and you'll usually place an even number of T pieces.

STMB Cave
The opener may be continued with a STMB Cave technique. S or Z piece is dropped horizontally on its counterpart to create a T-slot and O, L or J piece is placed vertically on the other side to create the overhang for a T-Spin. Eventually, this will result in 2 T-Spin Doubles. Only works if T piece comes late in second bag. If the pieces can be placed like shown in the pictures below, then there's a small chance to get a Perfect clear after 6 cleared lines.

S on S continuation
Another way to prepare a T-Spin Double is by placing S piece vertically on S piece (or Z on Z). A second T-Spin Double can be made at the end of the second bag. The O piece is either placed on S or Z piece.

If O piece is placed on S piece, then there's an 88% chance to get a Perfect clear after 8 lines. Those Perfect clear opportunities are hard to spot though; a piece is usually split by an in-between line clear.