Imp

Imp is a small zombie thrown from the back of the Gargantuar that can really cause you to lose the game, due to the fact that it get thrown into the middle of your plants and possibily at the final column, and can take up to nine shots to kill (for a Giga-Imp). It is very fast, but the weakest zombie too, the normal variety taking exactly 3 normal damage hits to kill, but those thrown from Gargantuars take 6 hits instead. However, if it is thrown deep into your defenses, it will most likely cause quite a lot of damage if your defenses are not internally strong enough. Imps are small enough to chew on a plant with a Spikeweed or Spikerock in front of it without being damaged. In I, Zombie, regular Zombies will eventually be replaced with Imps, so it may become necessary to use stronger zombies instead like the Conehead Zombie.

Strategy
When a regular Gargantuar is hit by an instant kill (but is not killed) or loses half of its health, it will throw the Imp off it's back approximately 6 squares forward. Covering the back three rows of land with Pumpkins is a good idea to protect against Imps. The fourth row might need a Pumpkin as well if an instant kill is launched when the Gargantuar just walked onto the lawn. In Survival :Endless, Gloom-shrooms with a laddered Pumpkin are often used as the Imp climbs over the ladder without hurting the Pumpkin and will be killed by the Gloom-shroom. Another method is to replace the Sunflower of the last column with plants, and the best choice is Melon-pult and Winter Melon because they can quickly kill the Imps and may also kill the Gargantuar. If there is not enough sun, replace the Sunflower with Twin Sunflower.

In the I, Zombie Puzzle Mode levels, although Imps can hardly withstand any damage, they're useful to send down an undefended lane to eat a Sunflower or a brain due to their speed. They can be also used to save sun, if any zombie is killed just before it eats the brain and then you use it. (although it may be killed at the same time).

Giga-Imp
Giga-Imps are Imps launched from Giga-Gargantuars. Like the Giga-Gargantuars compared to normal Gargantuars, Giga-Imps have 50% more health (9 hits) than those thrown by normal Gargantuars, so they take 3 more normal hits than ordinary Imps. They have almost as much health as a normal Zombie. They look no different than normal Imps.

Trivia

 * The Imp is one of the three zombies that has a Giga form, the other two being the Football Zombie and the Gargantuar.
 * It is also the only zombie that has a Giga that looks no different than the original one.
 * In I, Zombie, the Imp can survive a lane defended just by a Spikeweed due to its speed being faster than other zombies. However, one more normal pea, or anything that deals the same damage as a normal pea will kill it after it has passed the Spikeweed, so you´d better watch out for any Starfruit or Threepeaters.
 * In I, Zombie, the Imp is small enough so that if there's a Spikeweed or spikerock in front of a Wall-nut, the Spikeweed cannot attack the Imp while it is eating the Wall-nut.
 * The Imp's burnt head model is identical to that of the Catapult Zombie and the Zomboni,which is in spherical shape.
 * The Imp's head becomes smaller than its body when killed.
 * The Imp is one of only three zombies with feet that don't wear shoes, the other two being the Jack-in-the-Box Zombie and the Zombie Yeti. (This is assuming that Dr. Zomboss wears shoes, as his feet are not visible.)
 * If a Gargantuar that is carrying an Imp dies before throwing the Imp, the Imp will hide in the trash can it is riding in and will die with it.
 * This is similar to Dr. Zomboss hiding in the head of the Zombot when it gets destroyed.
 * The Imp has no standing animation as seen in the Suburban Almanac, same with the the Backup Dancer.
 * If a Ladder Zombie places its ladder on a Wall-nut, an Imp will not climb it, but will just pass through .This does not happen if the ladder is on a Tall-nut.
 * These zombies are the smallest of the zombies.
 * The Imp is the only zombie that sits down when it dies.
 * Apart from the Balloon Zombie over water and Jack-in-the-Box Zombies that explode without getting hit, the Imp has the least health among all the zombies.
 * If a thrown Imp is hypnotized by a Hypno-shroom, it may be able to eat the Garguantar that threw it, as the Garguantar does not crush the Imp.
 * The Imp, the Jack-in-the-Box Zombie, and Dr. Zomboss are the only zombies that smile. Although, the Jack-in-the-Box Zombie's face will be like a normal zombie once killed unlike the Imp which remains smiling.
 * When a Gargantuar throws an Imp, the Imp laughs.
 * If an Imp is thrown by a Gargantuar, it will be as slow as a normal zombie, although in I, Zombie, it is faster.
 * The Imp, along with the Football Zombie, the Zombie Yeti, and the old Dancing Zombie are the only zombies with normal feet (excluding the ones that don't step on land).
 * The Imp has to bite four times to kill a normal plant unlike most zombies.
 * The I, Zombie Imp is the second fastest zombie in the game, with the Dolphin Rider Zombie being faster.
 * If you look closely, the Imp is one of 3 zombies that show their tummy, other is Gargantuar, and Zombie Yeti (not counting the Giga-Gargantuar nor the Giga-Imp).
 * If you use an Ice-shroom while the Imp is in the air, the Imp will just become slowed down when it lands instead of freezing.