From Hard Drop  Tetris Wiki
Number One is a single bag opener discovered by player Riviclia that results in a platform TSpin Double. Thereby, the first T piece is spun into a vertical position like in STSD which makes it different from most other platform openers. It has quite some dependencies in the first bag (L after O, Z after S, J after I) but despite of its look it is a really good opener if applicable.
Contents 
Basic Setup
After the TSpin Double
There is a single floating mino in row 2 located on the right side. However, with SRS spins it is possible to fill the area beneath it, and prepare a TSpin Double as if the setup was just a regular STSD. Note that in diagram 3, the J piece must be spun 2 times to reach the desired location.
Instead of a TSpin Double, these are also possible:
TSpin Triple 

Perfect Clear continuations
6line PC
This continuation is invented by Agent RO. This continuation can be used if you get a Z piece before the O. There is a 95.24% chance to get a Perfect Clear after 6 lines.






With an early I piece in the third bag, the below may be used, but since there are several dependencies (T→S→L→I and Z→O), the above is more recommended.

TST TSD PC (8 lines)
The first continuation looks like a TSpin Triple setup but with an empty cell in row 2. So it just results in a TSpin Double and the empty cell can be used to prepare another TSpin. This continuation can be reached by spinning the J piece beneath the floating mino whereas there are 2 different paths; one where J is placed horizontally (diagram 3) and one where J is placed vertically (diagram 2).
 I → O and J → S → Z (98.17% PC rate, 39 solutions)



 I → O and J → SZ (90.40% PC rate, 13 solutions)



If making a Perfect Clear is not feasible, one can still make another TSpin using the remains.
Path 1 
Imperial Cross 
Path 2 
TSpin Triple 
Imperial Cross PC (8 lines)
The second continuation involves building an Imperial Cross with the remains of the STSD. There are 2 different paths again; one involving an LSpin (diagram 3) and the other involving a ZSpin (diagram 2).
 J → S and OL → Z (80.48% PC rate, 5 solutions)



 O → J → S and Z → L (80.28% PC rate, 7 solutions)



If making a Perfect Clear is not possible, one can make a TSpin Triple or Imperial Cross.
Path 3 
TSpin Triple 
Imperial Cross 
Path 4 
TSpin Triple 
Imperial Cross 
14line PC
There is no definite way when it is 14 lines. Below is an example with three Imperial Crosses and a 99.96% PC chance.











