  The Sprague-Grundy (SG) theory reduces the sum of impartial games to the
classical game of $NIM$. We generalize the concept of sum and introduce
$\cH$-combinations of impartial games for any hypergraph $\cH$. In particular,
we introduce the game $NIM_\cH$ which is the $\cH$-combination of single pile
$NIM$ games. An impartial game is called SG decreasing if its SG value is
decreased by every move. Extending the SG theory, we reduce the
$\cH$-combination of SG decreasing games to $NIM_\cH$. We call $\cH$ a Tetris
hypergraph if $NIM_\cH$ is SG decreasing. We provide some necessary and some
sufficient conditions for a hypergraph to be Tetris.
