From wiki
"Secret Grade" is a hidden grading mechanism in the TGM series that rewards creating a ">" shape by leaving holes in the stack.
At game over, the game evaluates the blocks in the field, looking for a zigzag pattern,
and it awards a "secret grade" ranging from 9 to 1 for up to nine rows of the pattern completed, S1 to S9 for up to 18 rows, or Gm for all 19 rows.
[edit] Basic Strategy
Creating the correct holes in the stack is easier to accomplish when a "sawtooth" or "stairs" structure is maintained in the direction of the diagonal you are creating. By maintaining this structure, holes can be covered with others to finish holes and create the foundation for new ones. S, Z, and T are very useful for creating the sawtooth structure or covering holes, although any piece can be used to create useful structures.
Line clears increment the level counter and can prevent progress. For these reasons, line clears are generally avoided. However, line clears can be useful or necessary in a variety of situations. Line clears are unavoidable when creating the first holes at either wall. If a line clear is necessary, holes can be built on top of the lines to be cleared and "dropped" into place.
Maintaining an even spread of pieces throughout the stack is very important. Uneven stacking can hinder the completion of holes and reduce placement choices near the top of the stack. Placement choices are limited near the top of the stack, so care should be taken to maintain an even stack without obstructions. If it appears that the stack is growing unstable, the best strategy is to clear lines or backtrack until a stable approach can be made.
Reaching the right wall is like starting over again; a line clear structure is needed to create the first few holes. Structures going to the right wall can be reused when returning to the left, but the pieces used must be flipped. For example, structures that used L before reaching the wall now use J on the return trip.
[edit] Starts
Starting the structure can be efficiently started with any piece but O. At least one line clear is required when using any other piece, but using O to create the first hole necessitates two.
