Threepeater

Threepeater shoots Peas in three directions: the lane above it, below it and the lane it's planted on. These are a handy middle-to-late game weapon, although it is best not to place them in the top or bottom rows, for they'll shoot two peas rather than their usual three. However, it is a good idea to plant them there after planting them in the middle rows.

Suburban Almanac Entry
Threepeater

Threepeater shoots peas in three lanes

Damage: normal (for each pea)

Range: three lanes

Threepeater likes reading, backgammon and long periods of immobility in the park. Threepeater enjoys going to shows, particularly modern jazz. "I'm just looking for that special someone", he says. Threepeater's favorite number is 5.

Cost: 325

Recharge: fast

Strategy
Since it fires down all three lanes whenever it sees anything in any lane, it can potentially hit zombies just as they enter the right side of the screen - well before other plants have noticed them. Its especially useful in conjunction with the Torchwood and on pool levels, since two Threepeaters in the second and fifth rows (both touching the sides of the pool) can cover all six lanes on a pool level.

Threepeaters have somewhat inaccurate animations and can actually hit zombies right above or below them. Because of this Threepeaters work better with Torchwood than the animation might suggest: if a Torchwood is planted directly above or below the Threepeater, the Threepeater will shoot fireballs directly out of its top or bottom head (respectively) without the peas even touching the Torchwood. Likewise, if a Torchwood is planted in the row above or below a Threepeater but one column ahead of it, the Threepeater's peas will turn into fireballs despite not having fully moved into the row and not having gone through the Torchwood.

It, paired with the Cherry Bomb, is a helpful weapon for earning the Pool's Closed Achievement, as it can help defend the pool lanes. Two would be recommended to ensure re-death of zombies.

Advantages

 * 1) Saves more space than 3 Peashooters.
 * 2) Only needs one Pumpkin to protect unlike 3 Peashooters which need 3 Pumpkins.
 * 3) Requires only one Lily Pad/Flower Pot.
 * 4) Can only be eaten on the lane which it is planted.
 * 5) Saves space

Disadvantages

 * 1) More expensive than three Peashooters (if you don't count the Lily Pad and Flower Pot) although only by 25 Sun.
 * 2) Can be eaten by only one zombie and when a zombie eats it, all three lanes become vulnerable.

I, Zombie
Threepeaters are encountered in various I, Zombie levels, including I, Zombie Endless. Like the Starfruit and Magnet-shroom the Threepeater is one of the few plants capable of affecting other lanes than the one its planted in. This allows the player to consider other lanes besides the one currently being assaulted. For example: an Imp about to walk down a seemingly undefended lane might still get killed by a Threepeater, wasting Sun. You may like to remove it with a Bungee Zombie. Overall, it is one of the top-tier threats of the level,the others being Starfruit, Magnet-Shroom, and Kernel-pult.

Air Raid
On the DS exclusive Mini-game Air Raid, the Threepeater is the upgrade for the Gatling Pea. The Threepeater will continue to shoot at the rate of a Gatling Pea, but now in three directions, for a total of 12 peas. If your Threepeater is not protected by a Pumpkin and it gets hit, it will revert back to the Gatling Pea. Picking up more than one at a time will not give you more hit points, and will still turn into a Gatling Pea after taking damage.

Trivia

 * If there is a Threepeater on the top or bottom row, the top or bottom head (respectively) does not have its firing animation play, as it cannot fire outside the screen.
 * If a Threepeater is in the top or bottom row, it will only fire two peas instead of three since there cannot be projectiles launched off screen.
 * If you play I, Zombie with a Threepeater at the top or bottom row, the top or bottom head respectively won't move at all as the paper cut-out plants will only move if there is a zombie.
 * The Threepeater's three heads bounce at different speeds. The bottom head bounces the slowest, while the middle head has an average speed, and the top head bounces the fastest.
 * Each head also has a different number of leaves on the back; the bottom one has one leaf, the middle one two, and the top one three.
 * The Threepeater is the most expensive non-upgrade plant in the game, costing 325 Sun.
 * The Threepeater is the only plant with three heads.
 * In the Xbox Trailer, when the person says, "You feel always safe", only Threepeaters are on your lawn.
 * The Threepeater, the Starfruit, the Cattail, the Cob Cannon, and the Gloom-shroom are the only plants that can fire outside the lane it is planted on.
 * If you observe carefully, you will see 3 peas coming out of the middle head only.
 * The Threepeater is obtained during a Pool level and thus, it is equal to three Peashooters and one Lily Pad.
 * Threepeater is one of the twelve plants that appear in the seed selection screen after you get the Grave Buster on the online version, the others are the Ice-shroom, Lily Pad, Potato Mine, Doom-shroom, Tangle Kelp, Jalapeno, Spikeweed, Torchwood, Tall-nut, Cactus and Blover.
 * The Lawn is flat yet the top head could hit the lane on the left and the bottom head could hit the lane on the right even though the heads are above and below the center head.
 * When the Threepeater shoots, the first pea goes forward as per normal, but the top and bottom peas come out from the middle then stay on that lane as if there is a swerve or curl.
 * Threepeater is a portmanteau of the words "three", in refernece to the number of heads, and "repeater", in reference to the number of peas it shoots.
 * The Threepeater is one of the six pea-shooters that can be attained in the game, including upgrades.
 * It is possible to beat a Pool level using only Threepeaters without any aquatic plants.
 * There is a DS achievement called Don't Drink the Water that can be obtained using this strategy.
 * The Threepeater has also the smallest head(s) out of all of the peashooters.
 * Threepeaters can be used to get Pool's Closed while playing Adventure Mode.
 * If the player did not purchase the full version of PvZ, the Threepeater cannot be used, but it still can be seen after you get the Grave Buster.