Pyromaniac

Strategy
The explosive plants are:


 * Cherry Bomb
 * Potato Mine
 * Doom-shroom (With Coffee Bean if needed).
 * Jalapeno
 * Cob Cannon (Multi-use explosive).
 * Ice-shroom

You can also use sun generating 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. Note: Wall-nuts, Tall-nuts, Pumpkins and Garlic don't count as plants that attack zombies as they defend (but don't use Wall-nuts and Tall-nuts because the Droid version will not award this achievement if you do). Graves don't count as zombies, as they don't move.

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, 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. 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 achivement much more easly than another way. The main difficulty of this acheivement is the recharge timer. 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 rake from Crazy Dave, you will not get this achievement until the rake disappears.

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, 16 Lily Pads, and 12 Wall-nuts. You can also get Defcorn 5.

Adventure
Choose the following plants:

The description says specificaly to use only explosive plants to KILL zombies, so fill in the rest of your seed slots with plants that don't kill zombies and might be usefull, such as Ice-Shroom. 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 stragtey, you will probably win the level and unlock the "Pyromaniac" achievment.
 * Potato Mine
 * Twin Sunflower (optional)
 * Sunflower
 * Potato Mine (Imitater)
 * Cherry Bomb
 * Doom-shroom
 * Coffee Bean
 * Jalapeno
 * Kernel-pult (if using Cob Cannon)
 * Cob Cannon (optional)

Trivia

 * This achievement does not appear in the DS version, because the mini-game, BOMB All Together!, has a similar concept.
 * Expert players can achieve it on survival modes.
 * The icon is used for one of the wiki badges.
 * A pyromaniac is someone who likes fire and explosives.