Although Gargantuar was a slow zombie, it had a high amount of health and could instantly destroy your plants by smashing them. Hypno-shroom, Garlic, Wall-nut, Tall-nut, and Pumpkin were useless against it. Once it was damaged enough, it would also throw its Imp. The player had to deal with its Imp, as well as the Gargantuar. Even if the player's defense is good on the Gargantuar, if they lack Imp defense, it will eat their plants and walk to their Roof Cleaners, or chimney.
Since no Bungee Zombies will steal the player's plants, three of them will drop additional ambush zombies instead. A Squash or Cherry Bomb is recommended to prevent them from eating the player's plants.
The objective, however, would not have been a big problem with Monk Flower.