Play as the Sunflower in Garden Ops mode under the easiest difficulty setting. Select the Garden Center map and pass the first wave without using any potted plants until only one zombie remains. Quickly plant a Scaredy Shroom plant and lure the zombie to it to scare it into eating it. Heal the Scaredy Shroom continuously to earn coins.
Flying Cactus
When you go into Garden Ops, place down a walnut barricade, or be on the edge of a wall. Then, deploy your drone, and fly under yourself. Then, while controlling the drone, you can fly yourself to an unreachable area, and unless someone shoots down your drone, you will be pretty much unreachable.