Pyromaniac

Difficulty: Hard-Very Hard (Easy in Buttered Popcorn)

Pyromaniac is an acheivement unlockable on iPhone, iPad, PlayStation Vita, Android, and Nook versions of Plants vs. Zombies.

Strategy
The explosive plants are: You can also use Sun producing plants as they don´t kill zombies but Lawn Mowers, Pool Cleaners, Garden Rakes and Roof Cleaners can't be used to obtain this achievement. You can't use other instants (except the Coffee Bean) like Blovers, Hypno-shrooms, Tangle Kelp, Umbrella Leaf, the Squash, and Chompers. Generally speaking, anything that shoots the zombies are not allowed (except for the Cob Cannon, although you could theoretically plant and upgrade or dig one before it shoots). If you attempt to plant a Cob Cannon, it requires two Kernel-pults, so only plant them when there are no Zombies in the same lane, or you won't be able to get this achievement because the Kernel-pults might kill a zombie.
 * Cherry Bomb
 * Potato Mine
 * Doom-shroom
 * Jalapeno
 * Cob Cannon
 * Ice-shroom

Note: Wall-nuts, Tall-nuts, Pumpkins and Garlic don't count as plants that attack zombies as they defend. Graves don't count as zombies, as they don't move, so you can use Grave Busters.

You can get this achievement in Quick Play. The easiest and best way to get this achievement is in Level 1-1. Choose Sunflower, Garlic, Jalapeno, Cherry Bomb, Doom-shroom, Imitater Doom-shroom, Coffee Bean, Potato Mine and whatever else you may want, that don't attack zombies. As the achievement states, you can only use explosive plants to kill zombies. Stockpile Doom-shrooms behind Garlic so they're safe you don't have to wait as long between uses. If you have shooting or lobbed-shot plants, you can't achieve this, but it isn't very different from any other level, so it can be beaten easily. Or just play 2-10 using only the Doom-shroom will gain the achievement much more easily than another way. The main difficulty of this achievement is the recharge time. Whenever a huge wave of zombies appear, place 2 Garlic on 2 lanes, and use a Cherry Bomb to blow up the zombies, but you'll get Explodonator first, instead of Pyromaniac. If you see too many zombies, use a Doom-shroom to blow them all up, but when you're in the final wave, divert more zombies, and use a Cherry Bomb and get the Money Bag, and you'll achieve this. You may also want to use Twin Sunflowers if necessary to rack up your total sun. A word of warning - if you have bought the Garden Rake from Crazy Dave, you will not get this achievement until the rake disappears.

Alternatively, it can be easily obtained in Level 2-1. Choose Sun-shroom, Cherry Bomb, Doom-shroom, Wall-nuts, Tall-nuts, Pumpkins, Potato Mine and Jalapeno. Kill the first 2 or 3 zombies with Potato Mines, while building 4 lines of Sunshroom. As soon as zombies start to come faster, slow them down with Wall-nuts, Tall-nuts, and Pumpkins and use a Doom-shroom to reset the situation when you attain 125 suns. Continue to setup until you reach 4 lines of Sunshroom, then you'll have plenty of sun to spam Cherry Bomb and Jalapeno. When a line is quiet (no zombies) put a preventive Potato Mine. When there are many zombies on screen, Doom-shroom to reset. If you can, add an Imitater Doom-shroom for additional power, but the level can be won without it.

It's also possible to get this achievement in other Adventure levels, but it will be quite a bit harder. Imitater instant kills can help.

In Last Stand you get enough Sun to plant 12 Kernel-pults, 6 Cob Cannons, 6 Lily Pads, and 12 Wall-nuts. You can also get Defcorn 5.

Adventure Mode
Choose the following plants: As said before, you can only use explosives to kill zombies, so don't buy the Garden Rake and make sure no zombies reach the Lawn Mowers/Pool Cleaners/Roof Cleaners. It is recommended to do the level on 1-1, if possible, because it is the easiest level. At the beginning of the level, plant a Sunflower at the top left corner of the lawn. Whenever you can plant a Sunflower towards the left of the lawn, but make sure you don't go past the second column. When the first zombie comes, plant a Potato Mine/Potato Mine (Imitater) ahead of him as much as you can. Do this for most of the zombies that approach. If there is a small group of zombies that you can't handle with Potato Mines, use a Cherry Bomb. If there is a lane with lots of zombies, use a Jalapeno. If there is a huge wave of Zombies, use a Doom-shroom and wake it up with a Coffee Bean. When you have around 700 Sun, plant a Kernel-pult, and quickly plant another in front of it, before they kill a zombie. Then, upgrade them to a Cob Cannon (don't do this until you have at least 700 Sun and the Cob Cannon is completely recharged). Using this strategy, you will probably win the level and unlock the "Pyromaniac" achievement.
 * Ice-shroom.
 * Sunflower
 * Potato Mine
 * Potato Mine (Imitater)
 * Cherry Bomb
 * Jalapeno
 * Doom-shroom
 * Coffee Bean
 * Kernel-pult
 * Cob Cannon

Alternative Method (Does not use Cob Cannon)
Choose to use the following plants: Do this on Level 1-1 or 1-2. Plant your Sunflowers in rows 1 and 5, upgrading them when you have enough Sun. When the first zombie comes, plant a Potato Mine as far back to the left as possible. After you gain enough Sun, begin planting Garlics in in column 2 of rows 1, 3, and 5. After this, begin to plant your stockpile of Doom-shrooms in row 3, then in the empty spots of 1 and 5. Use Coffee Bean to wake up a Doom-shroom, but remember not to go overboard and use Doom-shrooms to take out single zombies, using Potato Mines instead. Use the other instants when necessary, or when there are no Doom-shrooms. Plant Potato Mines, Wall-nuts, or Tall-nuts at the end of rows 2 and 4 as last resort protection. After this is set up, the game is a cakewalk.
 * Sunflower
 * Twin Sunflower
 * Potato Mine
 * Cherry Bomb
 * Jalapeno
 * Coffee Bean
 * Doom-shroom
 * Imitater Doom-shroom
 * Garlic
 * Wall-nut or Tall-nut (optional)

Another strategy
Load out with the following: This strategy is best used in 1-1 or 1-2. Just plant your Sunflowers and Potato Mines as you normally would. Then plant Garlic in every row except one. This will force all the zombies into one lane, so you can roast them with Jalapenos.
 * Sunflower
 * Potato Mine
 * Garlic
 * Jalapeno
 * If you want, Imitater Jalapeno
 * Other explosive plants you find necessary

Note: If you are going to use Cob Cannons to complete this, you must upgrade it quickly so the Kernel-pults don't kill anything.

Easy Method
You can also kill a zombie with a Potato Mine in I, Zombie to get this achievement. The Potato Mine makes its debut appearance in I, Zombie in the level Can You Dig It?.

Alternate Easy version(iPad only)
Completing the minigame Buttered Popcorn will get you this achievement if you don't use a Garden Rake.

Trivia

 * This achievement does not appear in the DS version, because the Mini-game BOMB All Together! has a similar concept.
 * A rake can be used in BOMB All Together!, despite not being an explosive.
 * The Mini-game Buttered Popcorn on the iPad version can get this easily, as long as you don't use a rake.
 * If you would really use Cob Cannons, it would be harder because the Kernel-pults are not instant kills.