Mountainous Stacking

Mountainous Stacking (also known as Mountain Stacking) is an opener that may result in a Perfect Clear chance after the T-Spin Triple in the second bag. It is created by Agent RO in mid-April 2021.

This opener has the same piece depenencies as Ito Cannon and Syrup Stacking. Similar to them, you need an early I and L. The difference between Mountainous Stacking and those two setups is that the first J piece will be used in various orientations to accommodate the sequence of your second bag.

First Bag
You can use this opener if you have an early I and L in the first bag. The J piece (L in the mirrored setup) is on Hold until the second bag.

Perfect Clear after 6 lines
Both methods here are invented by Agent 1568AH.

TSD Perfect Clear
This method involves keeping the L piece on hold, then place it after the T-Spin Triple, leaving with a 7.14% chance to make a Perfect Clear after a T-Spin Double or Single, while holding the S piece.

If you cannot make a Perfect Clear after 6 lines, place the S piece on L. You will still get a 53.41% success rate.

TSS Perfect Clear
For this method, the O piece should come before S and J, while holding the L piece. There will be a 21.43% chance in the third bag. The final 2 solutions may result in a T-Spin Single.

The success rate for 8 lines, while the L piece is on hold, is 96.55%.

Perfect Clear after 8 lines
In 98.06% of all second bags, one can use one of these 4 cases for a Perfect Clear chance. There will be a lot of piece dependencies, mainly for the fourth case.


 * S → JO (98.85% PC rate, 65 minimal solutions)


 * I → L and O → S (98.57% PC rate, 40 minimal solutions): This way of stacking the second bag is invented by Agent 1568AH.


 * O → I and L → S or S → JL (96.87% PC rate, 15 minimal solutions): For the first diagram, the first J is placed on the very right and the second J is used for the overhang.


 * I → O and LJ → S or S → JL (95.91% PC rate, 29 minimal solutions): The first J piece is used on the left first.

Compromise
There is a 1.94% chance that all the continuations above will not be possible because of the bag order, which in that case, one can always stack the compromise below, which has a 44.80% PC rate (one solution).

If you cannot achieve a Perfect Clear with the compromise, in most cases you will be able to stack the third bag depending on the order of the I, Z, J and L pieces, even if the O piece comes after S. In this case, you have a 35.71% chance to achieve a Perfect Clear after 10 lines.

Mountainous Stacking 2
Mountainous Stacking 2 is the successor to Mountainous Stacking. It is created by Agent RO. Like its predecessor, it is mostly used as a Perfect Clear setup. However, unlike its predecessor, the latter has no piece dependencies (the mirrored setup is also accounted) and there are fewer case differentiations in the second bag. This opener is fully developed in early May 2021.

Like Gamushiro Stacking, you can always stack this opener, if also accounting the mirrored setup. One advantage is that you will, in most cases, be able to stack either the first or second way of stacking the second bag and get a Perfect Clear chance, 97.94% at least. One disadvantage is that for the final two ways, it is mandatory to softdrop the Z piece. Overall, this is an alternative to Gamushiro Stacking when looking for higher PC rates.

The L piece (J in the mirrored opener) is on Hold until the second bag.

Second Bag and later
The second bag is stacked one of the 3 ways depending on the order of the I, S and O pieces. In the third situation, one can make a Perfect Clear after 14 total lines.


 * O → SI (99.09% PC rate, 63 minimal solutions): If the O comes early but not if it comes after I, which otherwise forces one to stack the third way, this is the case to stack.


 * S → O (97.94% PC rate, 19 minimal solutions)


 * I → O → S: The third bag can always be stacked even with an early I piece, and fourth bag can always be stacked, leading to a Perfect Clear chance (99.72% PC rate).