Mother earth launches an attack against the human race that is destroying here.
Things to do.
As a tumbleweed you attack crops and suffocate exhaust chimneys. The more you destroy civilization, the more natural vegetation grows back and the more tumbleweeds you have at your disposal.
There are environmentalists you can help, banksters you can lock in their house, and economies you can break by blocking roads.
Beware the fires that will quickly destroy your collected tumbleweeds. Rich industrialists will occasionally start large projects to combat you with enormous vacuum cleaners.
One last thing.
You can also let yourself be eaten by wild animals, hoping to create a plague.
Once the Dow Jones is at zero the rainy season starts and all tumbleweeds are washed away and go back to the earth.
Game ending 2.
If all humans are destroyed the tumbleweeds inherit the earth and come alive as tumblepeople. A strange folk with many annoying habits (arrogant!).
Game ending 3 (loosing).
If the tumbleweeds loose the human beings use geo-engineering to make the earth their bitch. She is transformed to resemble a giant clowns face. Variations: giant boob, baseball (and using it), giant hole in the center (using her for galactic ring throwing), entire surface filled with disco lights, carved out shapes so light of the center comes out.