Some of the zombies were pretty strong. The player would upgrade their plants before playing the level.
Upgrade your plants' power by playing previous levels. Then strengthen them even more with Puzzle Pieces and the Oven in your house. Hunt more Puzzle Pieces from previous levels.
The stronger attacking plants should be used here. Ice plants such as Snow Pea could be used to freeze enemies. Use defensive plants, such as Wall-nut, to protect other plants. You could also use other players' plants for stronger attack power and defense.