Unsiege Mentality

This is the DS equivalent of Grounded.

Strategy
For a more in-depth strategy, see Grounded

To get this achievement, play any Roof level and don't use any Lobbed-shot plants. Use shooting plants (like Repeaters, Threepeaters, etc.) on the 4th column from the left or Fume-shrooms on any column, as its fumes can be shot over the slanted part and onto the flat part.

Trivia

 * This achievement's image is a Cabbage-pult crossed out.