The basic concept is fairly simple -- there are two players,
one of whom plays a nearly standard game of tetris, the
other chooses which pieces his opponent will get.
Since play is asymmetric, a full game consists of two
rounds, with each player acting as the piece-dropper once,
and as the
piece-picker once.
Whoever has the higher score when playing as the piece-
dropper wins the game.
To avoid making the game either excessively hard or easy,
the piece chooser is initially quite constrained in how he
can dispense pieces, and these constraints are relaxed
slightly each time the piece dropper finishes a level (every
ten lines).
Of course, the game still speeds up with level completion,
just like regular tetris.
The piece chooser, playing on a separate computer from
the dropper, sees both the tetris 'well', and a piece
selection editor. On each row of the editor are seven
pieces, one of each tetromino. Pieces can be dragged left
or right on the line to make them occur earlier or later.
The piece dropper is dispensed tetrominoes from the top
row of the editor, leftmost first.
Each time the piece dropper is given a piece, it is darkened
in the editor, and cannot be moved. When an entire row is
darkened, it is removed from the editor, and a new row is
added to the bottom of the editor area, moving everything
up.
The above is not enormously different from how piece
choosing is restrained in the standard game of tetris.
Obviously normal tetris doesn't have someone maliciously
reordering pieces, but even so, it's possible for a skilled
piece dropper to play indefinitely, if he's got time to plan
ahead. Notably, the longest number of tetrominoes that
can occur between two 'I' pieces is 12, and the longest run
of consecutive 's' and 'z' pieces is 4.
Starting with level two, the rightmost column of the piece
chooser's editor gets greyed out. Pieces can still be
dragged there, but only the first six on each line will be
used. If the piece chooser wants, he can put all the 'i's on
the right, and never give them to the piece dropper.
On level two, an additional column in the piece choosers
editor is grayed out.
Etc..
On level six, the rightmost 5 columns of the piece choosers
editor are greyed out, which means that, if he wants, he
can give continuous alternating 's' and 'z' pieces to his
opponent, which has been mathematically proven to force
the game to end after at most 150 tiles, though in practice
happens much sooner.
On levels eight and above, the only thing which changes is
the speed of the game. Getting that far is unlikely, if the
piece chooser isn't stupid.
This idea was inspired by Hatetris (not to be confused with
Hatris), where the pieces are chosen by the computer, in a
non-random manner, to make it hard for the player to get
lines.