This level introduces the Zombie Fighter. If not taken down quickly, it could do considerable amounts of damage. Infi-nuts or Spinnapples are recommended in this level.
Strategies
This level introduces the Zombie Fighter. He will fire many bullets at the plants and potentially the house. While they do not do much damage, many can penetrate through defenses. In addition, he will loop back to the start if not defeated. It's recommended to use Spinnapple, as it can deflect his projectiles, as well as provide defense in the air.
With level 3-4 zombies, the player is bound to upgrade their plants. Zombie Fighters are more of a threat now due to them having triple or quadruple the health of a level one version of it. The same applies for the Bucketheads.
Strategies
Zombies come in fast, so be prepared and put out some plants quickly. The zombies are at Level 3, so plants should be right around that level as well. Zombie Fighters can give a little trouble, but with leveled up plants, it should be no problem.
The small number next to the zombie icon means that zombie will always appear in that lane, with 1 being the topmost lane and 5 being the bottommost lane.