Gargantuar

Gargantuars are the third strongest zombie in the game (with only Dr. Zomboss, the Giga-Gargantuar is stronger, the Giga Football Zombie has the same health), taking two instant kills to destroy. It is the third last zombie in Adventure Mode. Not only does this massive land zombie have high health, but he also crushes the player's plants instead of eating them. Because the Gargantuar can crush plants, it is capable of destroying Spikerocks and Spikeweed. Upon dying, Gargantuars drop their Telephone Pole, Crossing Sighn, etc, roar, sway, and fall over. Once it has lost half of its health (or been attacked by an instant kill) it will throw an Imp - assuming it is less than half way across the screen.

Suburban Almanac Entry
 Gargantuar 

Gargantuar is a gigantic zombie.

Toughness: extremely high

When Gargantuar walks, the Earth trembles. When he moans, other zombies fall silent. He is the zombie other zombies dream they could be. But he still can't find a girlfriend.

Overview
Absorbs 150 Normal Damage shots. Appearance changes after 50 and 75 Normal Damage shots before dying at 150 Normal Damage shots, or 2 instant kills.

Strategy
You can delay a Gargantuar with Spikerocks, which take nine smashes before they disappear. Cheap plants like Puff-shrooms are also a good choice, as they have fast recharge and cost no sun so are good emergency delayers. It is advised that you attack it with at least one instant, or else it may do a lot of damage to your vital defenses. Winter Melons are quite useful, especially in Survival Endless, although Chompers cannot eat a Gargantuar whole, they can keep biting at it, doing four damage per bite. Hitting a Gargantuar with a Squash followed by a Jalapeno kills it fast, and prevents the Imp from doing serious damage. A charged Potato Mine will deal damage to the Gargantuar when it crushes it. Hypno-shrooms do not work against it, because it does not try to eat anything. However, a hypnotized Imp can eat a Gargantuar without dying. Rows of Gloom-shrooms adjacent to his path will work as well. In the Survival Mode Pool levels (especially Survival: Endless) you can stagger it a bit so that Gloom-shrooms in the pool kill Gargantuars before they reach ones on dry land. It is also useful to know that it takes several hits for a Gargantuar to smash a Spikerock.

I, Zombie
In the I, Zombie level Me Smash!, these are useful in hard rows without multiple Squashes, although occasionally a single Squash and a Kernel-pult with other offensive plants can kill it too.

Vasebreaker
In Vasebreaker, save some Squashes to get rid of these zombies, though Potato Mines work as well. There will be a Gargantuar but it might be difficult as the Squashes will go away after some time and clicking randomly until the Gargantuar appears might outnumber your other lanes.

Killing them
Probably the most useful strategy for Gargantuars, working well in both Dr. Zomboss's Revenge and Column Like You See Em', is using 2 Jalapenos, one to activate the Imp and another one to take them out without major damage from the Imp.

Giga-Gargantuar
The Giga-Gargantuar is the second most powerful zombie in the game, found only in Survival: Endless, Survival: Day (Endless), Survival: Night (Endless), Survival: Fog (Endless), and Survival: Roof (Endless). It has double the health of a regular Gargantuar, making it able to take 300 normal damage shots or four instants. To prevent confusion, the Giga-Gargantuar has sour red eyes. One can take four instants, which means the Cob Cannon is a good plant to have in your arsenal. It is also a good idea to pack extra instant kills such as Squash, Jalapenos, Potato Mines and Cherry Bombs. After two instants or 150 normal damage shots, a Giga-Gargantuar will hurl an Imp into your defenses, unless it is already halfway into your lawn. These Giga-Gargantuars do not have almanac entries. Try to pack in as much instant kills as you can such as Cherry Bomb, Jalapeno, Potato Mine, Cob Cannon, Squash and Doom-shroom (with Coffee Bean). In Survival: Roof (Endless), the Giga-Gargantuar will appear before a normal Gargantuar appears.

Trivia

 * A Lawn Mower and a Roof Cleaner can kill a Gargantuar, despite the size of the Gargantuar. When it is killed by one, the Gargantuar turns into a puff of smoke even though the Gargantuar is not mechanical.
 * This could be because Gargantuar(s) have no "head falling off" animation. It would also seem ridiculous if it dies the normal way (drop club, stagger, fall down and die) when hit by a lawn mower (actually both seem ridiculous, but exploding seems better and more appropriate than the normal death).
 * The Gargantuar somewhat resembles the boss Death from House of the Dead 3.
 * Despite the Almanac saying that the Earth trembles when Gargantuar walks, the whole screen does not shake when he takes a step.
 * In the I, Zombie level Me Smash!, the Gargantuar squashes the brain instead of eating it.
 * However, there is a biting sound when this happens. The same sound is also played after it kills a plant. This is because the Gargantuar has no eating animation.
 * This is also played when a Zomboni, a Catapult Zombie, or Dr. Zomboss's Fireball/Snowball attack kills a plant, or when the Zombot's foot/camper crushes other plants.
 * According to its almanac entry, the Gargantuar is the only Zombie who is looking for love.
 * The Gargantuar is the second most expensive zombie in the puzzle I, Zombie, costing 300 Sun.
 * The only zombie which costs more in I, Zombie is the Dancing Zombie, which costs 350 sun.
 * If the Gargantuar is killed by an explosive and hasn't been able to throw its Imp, the body of the Imp will also disintegrate inside the trash can and then its head will fall onto the pile of ash the Gargantuar has turned into.
 * If the Gargantuar is killed (not by explosive instant kills) while in the process of throwing an Imp, the Imp will recede back into its trash can.
 * The Gargantuar will not hit other zombies that have been affected by a Hypno-shroom. Instead, the Zombie will just die. (except its thrown Imp)
 * If a Chomper manages to kill a Gargantuar, it will show the chewing animation with a normal zombie's arm sticking out.
 * The Gargantuar, the Zomboni, Dr. Zomboss, the Giga-Gargantuar, the Catapult zombie and the Squash Zombie are the only zombies that can crush plants.
 * If a Gargantuar is killed while slowed by some sort of ice plant right at the starting point you will be able to see the corpse while you are picking plants (Survival Mode only.)
 * After the Gargantuar has half of its health gone, bandages will appear on its body.
 * The Gargantuar smashes and crushes the plants, similar to what the Squash does to zombies.
 * Gargantuars can have one of three different clubs: a telephone pole, a wildlife crossing sign, or another zombie.
 * The zombies that the Gargantuars use have cut ties on their clothes.
 * Gargantuars only use normal zombies as clubs.
 * Their hand's graphics seem to be designed specifically for the telephone pole, as for other clubs their fingers partially overlap the sprite of the wildlife crossing sign or zombie.
 * The name Gargantuar likely comes from its gargantuan size or possibly as a reference to the Toho movie "The War of the Gargantuas".
 * It is also possible that Gargantuar's name may be a reference to the fictional giant Gargantua.
 * Gargantuars can only throw its Imp 4 squares away from the right side of the screen. If a Gargantuar loses half of its health at the fifth square, it can't throw an Imp.
 * The Gargantuar is one of the three zombies that have a Giga form. The other two are the Imp and the Football Zombie.
 * The Gargantuar is one of the three zombies that comes in groups, the other two are the Zombie Bobsled Team and the Dancing Zombie with its Backup Dancers.
 * When a Gargantuar throws an Imp while it is frozen/slowed down, the Imp will also be slowed down.
 * If the Giga-Gargantuar is killed by an explosive (i.e. instant kill), his eyes will be white instead of red.
 * The Gargantuar, the Giga-Gargantuar, the Bungee Zombie, the Balloon Zombie above the pool, the Zomboni, the Catapult Zombie, and Dr. Zomboss are the only zombies whose heads don't fall off when killed or defeated.
 * When the Gargantuar smashes a plant, the whole screen shakes.
 * The screen also shakes when the Gargantuar's dead body hits the ground.
 * It also happens when the Squash squashes any zombies.
 * This also occurs when Cob Cannon's cob explodes
 * When using the Action Replay on the DS version, a glitch may occur in which when the zombies are viewed, the Gargantuar will be seen without a head, the Imp at its back, and its legs.
 * The Imp on the Gargantuar holds reins tied to the Gargantuar's collar but when he throws the Imp the reigns disappear.
 * A rake alone will not kill a Gargantuar,it will deal one instant kill of damege but he will throw the Imp.
 * The Gargantuar's roar is the same roar used by Dr. Zomboss when his Zombot is destroyed.
 * It takes 6 hits in Co-Op Wall-nut Bowling.
 * The Zombot looks like it is based on a Gargantuar, considering the toughness and appearance of both zombies.
 * The Gargantuar, the Balloon Zombie and the Screen Door Zombie are three of four zombies that appear in a normal I, Zombie level, but not in I, Zombie Endless. This is probably to keep the player from making the puzzle too easy, due to the fact that these three are super-effective against the plants in the level. However, the normal Zombie is also omitted to make the game more challenging in another way, for a normal Zombie can sometimes manage to clear a line with a single offensive plant, while the Imp cannot in most cases, unless the offensive plant is a Spikeweed or (sometimes) a Kernel-pult in the rightmost column.
 * It is possible for a Gargantuar to be damaged by a Spikeweed or a Spikerock, if you plant it under the Gargantuar.
 * If a sleeping mushroom is squashed by a Gargantuar or Dr. Zomboss' trailer, the mushroom will become a flattened woken version of the mushroom.
 * The Imp may be the Gargantuar's master, since it is shown holding strings attached to the Gargantuar's neck.
 * Gargantuar's toes are visible at some point. They stick out of his shoes.
 * The Gargantuar may be a reference to Shrek since they look like ogres.
 * Since Gargantuars don't eat, it is odd that the eating sound is played if it successfully invades the house.
 * Despite the fact that the zombies in the game were once humans, it doesn't make sense how a Gargantuar could have a been a human due to its massive size.
 * Gargantuar, Giga-gargantuar, Giga Football Zombie, Tall-nut Zombie and Dr. Zomboss are the only zombies that can survive an Instant kill.
 * The Gargantuar has a collar around its neck.
 * Maybe because the Imp thinks the Gargantuar is its pet.
 * Or maybe Imp just wants to tag with Gargantuar so that he can get a piece of the action, and needs a safe and stable platform to see all around him. It is also possible that they are best friends and Gargantuar drags him along, as a favour.
 * You can kill a Gargantuar before he launches Imp, if you find a two fully-charged instant kills or explosives.
 * The Gargantuar can only have two Band Aids.
 * Why Gargantuar throws Imp is unknown. It is possible that he is so angry at being wounded, he needs somebody to take his anger on, or simply on Dr. Zomboss's orders.
 * When a Gargantuar squashes a Sunflower in the I, Zombie level "Me Smash!", all the sun comes out, unlike the other zombies in I, Zombie, as they eat the Sunflower while sun comes out.
 * The Gargantuar and Imp may be a reference to Freak the Mighty, where Freak rides on Max's shoulders like an Imp rides on a Gargantuar's back.