Each player starts controlling a square. There are three different
control levels: 1, 2 and 3. You can take over empty squares at any
time, but you can't take over other people's squares by just
clicking on them. When you click in a square with level 3, it'll
explode and contaminate the nearby squares, depending on how each
one is occupied: if it's empty, you'll get a level 1 square, if
another player is occupying it the square will keep a level
calculated by (3-current_level) (for example, if you contaminate a
level 3 square, that square will become empty, but if you contaminate
a level 1 square you'll win a level 2 square). If you contaminate a
square that you already control its level will increase by one unit
(this can lead to some interesting chain reactions). Sometimes bombs
are dropped on the board. They will explode if they're contaminated
or clicked and destroy everything that surrounds them. The last player
standing wins the game.
Note: in the Expansion Game you can only place a new piece
if you already control a nearby square.