This level introduces the Imp Cannon. The Imp Cannon stays at the back and launches Imp Pirate Zombies for a while before exploding and raining down more of them if not dealt with. Luckily, they only appear on rows without planks in this level. Projectile based plants can kill it easily. However, Barrel Roller Zombies appear yet again, so the player should not rely on just those types of plants.
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 one.
When a zombie appears, plant a Spring Bean. Later, you will see that it bounces that zombie into the water as an instant-kill plant. Try to plant one more Spring Bean to take out another zombie.
Do not forget to build your offense; Two columns of Repeaters and one column of Snapdragons.
Wall-nuts are still needed due to Snapdragon's range. You still have to be careful of Barrel Roller Zombie. However, do not worry because the Spring Bean's Plant Food upgrade will take care of all the zombies near the water, including the barrel.