Ladder Zombie

Ladder Zombie, similar to the Screen Door Zombie, carries a shield in the form of a ladder and is the 21st zombie encountered in Adventure Mode. It moves faster than other zombies when it has its ladder. In addition to its function as a shield, the Ladder Zombie can use its ladder to get over the first defensive plant (Wall-nut, Tall-nut, Pumpkin, or an imitated version) it encounters. It leaves the ladder behind so other zombies can also climb over the defensive plant, then continues at a normal speed to eat the remaining plants. Ladder Zombie can eat other plants, even if it encounters them before placing the ladder. For example, if the player has a Sunflower in front of a Tall-nut, it would eat the Sunflower, place the ladder on top of the Tall-nut, climb over the Tall-nut, and keep going.

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
Ladder Zombie absorbs 42 normal damage shots, and its appearance changes upon absorbing 9, 17, 25 (when the ladder is destroyed), and 34 normal damage shots before dying at 42 normal damage shots.

Ladder Zombie loses its ladder upon placing it to get over a defensive plant, therefore losing the remainder of the ladder's hit points. Any damage that Ladder Zombie itself sustained (from lobbed projectiles, fumes, Spikeweeds, Spikerocks, or projectiles from behind) remains in place.

Encounters

 * Adventure Mode: 5-3, 5-4, 5-5, 5-7, 5-9, 5-10
 * Mini-games: Column Like You See 'Em, Last Stand, Dr. Zomboss's Revenge, Buttered Popcorn, BOMB All Together!, Bungee Blitz
 * Puzzle Mode: Totally Nuts, Three Hit Wonder, All your brainz r belong to us, I, Zombie Endless, Last Stand: Roof, Last Stand Endless
 * Survival Mode: Survival: Fog, Survival: Roof, all Survival (Hard) and Survival (Endless) levels
 * Co-op Mode: all Co-op Hard levels, Co-op Zomboss, Co-op Endless
 * Others: Versus Mode

Strategies
Ladder Zombies can be annoying because they can easily get over your defenses, also letting other zombies do so too. However, there are various ways to deal with this zombie. The ladder can be taken away by a Magnet-shroom, even if the ladder was already placed. Instant kills, (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, Spikerocks, 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 deal 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 the zombie 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 you shouldn't 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 untouched (passed over) while still eating zombies. This works especially well if the Chompers are planted on the right side (forefront) of the lawn/roof, but obviously not very well if planted too close to house.

I, Zombie
When used properly, Ladder Zombies can quickly overrun rows with large amounts of Peashooters and other similar plants. You should consider using Ladder Zombies instead of Bungee Zombies to render useless Wall-nuts or Tall-nuts, rather than send plenty of zombies to get over the defensive plants. However, don't use them near Magnet-shrooms, as they will remove or steal 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 to compensate for the lower health. Above everything, avoid placing Ladder Zombies in rows with Kernel-pults, Spikeweeds, or Fume-shrooms, as they will die quickly from the direct damage. Usually when Snow Peas are around, they work better than Football Zombies, being fairly cost-effective (150 sun for Ladder vs. 175 sun for Football).

On very well defended lanes with Snow Peas, where a single Ladder Zombie would not complete the lane and get the brain alone, they can work well by teaming them with a Football Zombie. They work well when they are both near, with the Ladder Zombie first, which's role is protecting its Football Zombie partner from frozen peas. Usually, when both of them will encounter a plant and eat it at the same time, Football Zombie's hitbox will cover the Ladder Zombie's one, freezing the Football Zombie, but it does not matter because after the plant disappeared, Ladder Zombie will walk faster than his partner but, protected from frozen peas, it will finally get his normal speed back and get to the Ladder Zombie again when this one will be stopped eating a plant. This team often works better than two Football Zombies together. It also costs 25 sun less.

To be extremely economical, a Ladder Zombie can also pair up with another low health Zombie, for example Pole Vaulting Zombie. When the Ladder at hand degrades for the second time, send off the Pole Vaulter to quickly catch up the battlefront, who either sacrificially absorbs damage and saves the Ladder Zombie, or ends up surviving (typically benefited from vaulting over one plant) and finishes the row. This strategy is meant to reduce the cost (down to 225 sun or so) for the row of interest.

Trivia

 * Ladder Zombie is one of the two zombies that has a shield used for something more than just protection, the other being Excavator Zombie.
 * The ladder is a shield against head-on projectiles. It provides no protection against fume attacks, arcing catapult projectiles, attacks from below (such as those from Spikeweed and Spikerock), attacks from the back (e.g. behind a laddered Split Pea), and explosives.
 * It shares this trait with the Screen Door Zombie and the Newspaper Zombie.
 * Ladder Zombie is the only one of these three to not be introduced in the Night stage.
 * Ladder Zombie is the only zombie that is told to have money, since the Almanac entry states that it bought the ladder for $8.99.
 * This seems to be underpriced for a ladder.
 * Ladder Zombie is one of the few shield zombies that lose their arm while they still have their shield, the other being Excavator Zombie.
 * Ladder Zombie only puts his ladder down when he reaches a Wall-nut, Tall-nut, or Pumpkin, but not when reaching a Garlic.
 * Ladder Zombie will not eat defensive wall plants when its ladder is intact.
 * A ladder will disable but not destroy one defensive wall plant. Most zombies approaching from the right side of the screen will climb over it. A Digger Zombie approaching from the left will still attack a defensive plant with a ladder attached.Black ladder.PNG
 * Unlike Newspaper Zombie and Screen Door Zombie, the ladder protects hypnotized Ladder Zombies.
 * Even if the Ladder Zombie loses its ladder, it won't still use its hands to eat plants like of most of zombies do.
 * The same thing happens with Newspaper Zombie.
 * Ladder Zombie actually eats further away from plants than other zombies. This also occurs with Newspaper Zombies.
 * In the DS version, even if the ladder is damaged, while the Ladder Zombie is eating, it appears to be undamaged.
 * A placed Ladder can be destroyed by an explosive (Cherry Bombs, Jalapenos, Doom-shrooms, Cob Cannons, and Potato Mines) or by digging up the plant that it is placed on. Placing a Magnet-shroom within range will remove ladders, even if they have already been deployed.
 * If the player kills a Ladder Zombie in the progress of placing a ladder, its head will fall off, stop, and fall. The ladder will also disappear.
 * Even if the ladder has taken damage, the ladder will look undamaged when placed on a Wall-nut, Tall-nut, or Pumpkin.
 * Ladder Zombie, Imp (while flying), Balloon Zombie (while using its balloon), Digger Zombie (while digging), Gargantuar, Zomboni, and Catapult Zombie are the only zombies that can get past a Tall-nut by itself without eating the plant.
 * The Gargantuar, Zomboni and Catapult Zombie crush the Tall-nut instead.
 * Even if Ladder Zombie's ladder is undamaged, it will change appearance to look damaged if the zombie dies while carrying it. The same thing happens with the Screen Door Zombie and Newspaper Zombie.
 * Ladder Zombie has a pencil stuck in the side of its head, a tool belt with a hammer, and a plaid workman's shirt.
 * Ladder Zombie has the same speed as the Pogo Zombie while holding his ladder. If he loses his ladder (deployed, magnet, broken), he slows down to the speed of a normal zombie.
 * 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 deployed.
 * When an Ice-shroom is activated or a plant is upgraded inside a Pumpkin with a ladder, it is destroyed.
 * Another cause of disappearing ladders against Pumpkins is removing the plant inside the Pumpkin.
 * Ladders are sometimes used in strategies in Survival: Endless to make plants invulnerable to eating zombies.
 * Ladder Zombie, the ZomBotany Zombies, Dancing Zombie, and Jack-in-the-Box Zombie are the only zombies that can use their abilities when hypnotized.
 * There is a glitch that sometimes Ladder Zombie's arm will not fall off, but the bone is still shown. This gives the appearance of the bone sticking out of the arm.
 * Ladder Zombie is the only shield zombie that can lose its shield without it or the zombie being destroyed.
 * In comparison with the graphics on the DS(i) version to other versions, the Ladder Zombies seems to be slightly faster, making it a bit more dangerous (especially if playing Dr. Zomboss's Revenge). However, it still retains the same amount of health as all other versions.
 * Ladder Zombie is one of the four zombies in the whole series that has the first letter L. The others being Landscaper, Long Bomb and Leprechaun Imp.
 * Ladder Zombie is one of the three zombies that does not appear in Plants vs. Zombies 2 but appears in Plants vs. Zombies: All Stars. The other two are Pole Vaulting Zombie and Football Zombie.
 * Ladder Zombie is mentioned (albeit called a "zombie with a ladder") in Charlie Higson's novel The Fallen, when one of the characters writing in her diary says how she used to be scared of this zombie when she played Plants vs. Zombies on her father's phone before the disaster happened.
 * Ladder Zombie has the same shirt as Target Zombie.