You're heading to the Last Stand Minigame and selecting the Garlic, Lily Pad, Marigold, Pumpkin, Magnet Shroom, Gold Magnet, Fume Shroom, Gloom Shroom, and Coffee Bean.
Next, place all the plants as shown in the video. Remember to wake up the Fume Shrooms with a Coffee Bean and then upgrade them to Gloom Shrooms. To get the Gold Magnets, you need to first place Magnet Shrooms and then place the Gold Magnets on top of them (you don't need to wake up the Magnet Shrooms).
At the beginning, you won't have enough money to place 8 Pumpkins, but after the first wave, you'll have enough suns for that. After the second wave, you'll even have enough for two extra Pumpkins. Eventually, some Pumpkins will get destroyed, so it's recommended to replant them.
It's necessary to replace the Garlic after each wave, as they are gradually eaten.