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The level has different hard-to-defeat zombies like Zomboni, Jalapeno Zombie and Gargantuar. Therefore, without strong plants, this level will be difficult.
Plant your sun-producing plant. With a high-level Monk Flower it's enough to save up for Melon-pult at the start of the game. Plant Snow Peas on the flat ground if needed.
Protect your plants with four Umbrella Leaves. Move the Monk Flower to the Umbrella Leaf as Heroes does not deactivate Umbrella Leaf's function.