Ladder Zombie

The Ladder Zombie, similar to the Screen Door Zombie, carries a shield in the form of a ladder (hence the name). It moves quickly and uses a ladder to get over the first defensive plant (Wall-nut, Tall-nut, or Pumpkin) it encounters and leaves it there so other zombies can use it, then continues at normal speed to eat the remaining plants. The Ladder Zombie can eat other plants, even if it encounters them before placing the ladder. For example, if you have a Sunflower in front of a Tall-nut (which would be a bad idea), it would eat the Sunflower, place the ladder on top of the Tall-nut, climb over the Tall-nut, and keeps going. It is similar to a Pole Vaulting Zombie, but eats faster, only uses the ladder on defensive plants, can go over Tall-nuts, has more health, and allows other zombies to climb over defensive plants. He is the 21st Zombie you will encounter in Adventure Mode.

Suburban Almanac Entry
 Ladder Zombie 

Ladder Zombie climbs over obstacles.

Toughness: medium

Ladder Toughness: medium

Speed: fast, then slow (after placing ladder)

Weakness: fume-shroom and magnet-shroom

He picked the ladder up for $8.99.

Overview
Absorbs 42 normal damage shots. Appearance changes upon 9, 17, 25 (at this point, his ladder is destroyed), and 34 before dying at 42 normal damage shots.

Strategy
Ladder zombies can be annoying, because it can easily get over your defense, also letting other zombies to do so too. However, there are various way to deal with this zombie. The ladder can be taken away by a Magnet-shroom, even if the ladder was already placed beforehand. Explosive plants, (Cherry Bombs, Jalapenos, Doom-shrooms, and Cob Cannon cobs) will also destroy the ladders after they are placed. These zombies are also weak to Fume-shrooms, Gloom-shrooms, Spikeweed/Spikerock, and lobbed-shot plants, (the lattermost of which should compose the majority of your offense in the Roof levels in which the Ladder Zombie appears) as they do direct damage, and do not have to destroy the ladder first. The ladder can also prove to be a weakness to the Ladder Zombie, as Split Peas, Starfruits, and Gloom-shrooms can shoot backwards to damage it directly, making it a good idea to plant them in Pumpkins. This would effectively make the plant invulnerable, until an explosive plant or Magnet-shroom is utilized; so do not use both of these techniques at once (or near each other). Of course, this would not be helpful against Gargantuars, or Zombonis. Ladders are best for a Chomper inside a Pumpkin, since the Chomper will be left uneaten by Zombies, while they still can eat the Zombies, (not including the one planted furthest to the left). This works especially well if the Chomper is planted on the right side of the lawn.

I, Zombie
Ladder Zombies cost 150 sun. You should use Ladder Zombies to climb over Wall-nuts or Tall-nuts instead of sending plenty of zombies to get over the defensive plants. However, don't use them near Magnet-shrooms, as they will remove the ladder. If there are no defensive plants in a row, they can be a usable substitute for the Screen Door Zombie, with a shield to protect against the freezing effects of Snow Peas, and faster movement and chewing speeds to compensate for the lower health.

Trivia

 * Unlike the Newspaper Zombie and the Screen Door Zombie, the ladder protects hypnotized Ladder Zombies.
 * Both the Newspaper Zombie and the Ladder Zombie eat without using their hands.
 * The Ladder Zombie is the only shield zombie that has a shield used for more than protection.
 * The Ladder Zombie only puts its ladder down when it reaches a Wall-nut, Tall-nut, or Pumpkin, but strangely, not when reaching a Garlic.
 * A placed Ladder can be destroyed by an explosive (Cherry Bombs, Jalapenos, Doom-shrooms, and Cob Cannon cobs). It can also be destroyed by digging up the plant that it is placed on.
 * The Ladder Zombie actually eats further away from plants than other zombies. This also occurs with Newspaper Zombies.
 * There is a glitch in that if a Ladder Zombie loses its arm, the arm will not come off and you can see a bone sticking out of its knee.
 * If you kill a Ladder Zombie in the progress of placing a ladder, its head will fall off, stop, and fall. The ladder will also disappear.
 * The Ladder Zombie and the new Backup Dancer are the only zombies with mustaches (if the "Mustache" mode is off).
 * Even if the ladder has taken damage, the ladder will look undamaged when placed on a Wall-nut, Tall-nut, or Pumpkin.
 * The Ladder Zombie, the Imp (while flying), the Balloon Zombie (while on its balloon), the Digger Zombie (while digging), the Gargantuar, the Zomboni, and the Catapult Zombie are the only zombies that can get past a Tall-nut by itself without eating the plant.
 * There is a glitch that when a Magnet-shroom behind a Tall-nut or in a Pumpkin steals the ladder, the zombies can still climb over the Pumpkin or Tall-nut, as if the ladder was placed there.
 * Even if the Ladder Zombie has its ladder undamaged, the ladder will look damaged if the Ladder Zombie dies with his ladder. The same thing happens with the Screen Door Zombie.
 * The zombie has a pencil stabbed on his head. Possibly this zombie was a construction worker.
 * However, in the DS version, it looks more like a scar.
 * The Ladder Zombie is one of the key Zombies in All your brainz r belong to us — it should be used on rows with Tall-nuts.
 * The Ladder Zombie, for some reason, moves faster holding the ladder, as it seems it would be considerably heavy.
 * This may be true because the Ladder Zombie's purpose is to put ladders on defensive plants, and it wants to do that faster.
 * Some ordinary ladders cannot be stolen by magnets (or in this case, Magnet-shrooms, due to the fact that they are made of aluminum).
 * The Ladder Zombie will not eat defensive plants when he has his ladder intact.
 * The ladder is actually an shield, but like a Newspaper Zombie and Screen Door Zombie, he has a weakness - Fume-shrooms and Gloom-shrooms.
 * Ladder Zombie may be somewhat related to Larry the Cable Guy.
 * The Ladder Zombie is the only shield zombie that loses his arm while he still has his shield.
 * The Ladder Zombie has the second shortest Almanac Entry. The Dolphin Rider Zombie has also the shortest Almanac Entry.
 * The ladder can be called an instant kill because it kills defensive plant automatically, since all zombies with climb over it.
 * Ladder Zombie can climb Wall-nuts, Tall-nuts, or Pumpkins.
 * But actually, that defensive plant can stop Digger Zombie from the other side.
 * The Ladder Zombie has the same speed of the Pogo Zombie.