Tangle Kelp

The Tangle Kelp is a one use, instantly armed aquatic trap, dragging any zombie unfortunate enough to cross its path to the watery depths into the Pool.

Usage
Place a Tangle Kelp in any water lane, and it will take down the next single Zombie that touches it. Note that it cannot kill zombies behind it, so make sure when the final wave happens that it is far enough back that zombies won't surface behind it.

Suburban Almanac Entry
Tangle Kelp

Tangle Kelp are aquatic plants that pull the first zombie that nears them underwater.

Damage: massive

Usage: single use, on contact

Must be planted in water

"I'm totally invisible," Tangle Kelp thinks to himself. "I'll hide here just below the surface and nobody will see me." His friends tell him they can see him perfectly well, but he'll never change.

Cost: 25

Recharge: slow

Strategy
With such a low cost, Tangle Kelp makes an ideal early defense in pool lanes. Just don't get lulled into failing to build up your pool defenses, because the slow recharge prevents Tangle Kelp from being readily re-used.

They also take down Dolphin Rider Zombies whole instead of being jumped over, so these may be more useful than just placing a Lily Pad in front of it. Furthermore, they are useful in defeating Snorkel Zombies, as they can drown them without having them come up. However, their slow recharge may prevent them from drowning every Dolphin Rider Zombie or Snorkel Zombie, so it's wise to prepare backup plans for them just in case.

Trivia

 * The Tangle Kelp and Chomper are the only Instant Kills that are not Area of Effect plants.
 * The Tangle Kelp is the only attacking plant that Dolphin Rider Zombies can't jump.
 * Along with the Sea-shroom, the Tangle Kelp is one of two offensive plants that don't require Lily Pads to be in the Pool.
 * The Tangle Kelp, the Sea-shroom, the Grave Buster and the Cob Cannon are the only plants that cannot have Pumpkins placed around them, excluding the Pumpkin itself.
 * The Tangle Kelp cannot tangle the Bungee Zombie and make him drown.
 * When being stolen by a Bungee Zombie, the Tangle Kelp still animates its ripple animation on the air.
 * It´s unknown how the Zombies can drown, as they don't have to breathe, which is stated in the description of the Snorkel Zombie.
 * However, they might be strangled to death by the Tangle Kelp.
 * Then again, zombies might not die due to strangulation. Instead, the Tangle Kelp could have just cut his head off.
 * The Tangle Kelp, the Chomper, the Potato Mine, and the Squash are the only Instant Kills that are used on contact with the enemy.
 * The Tangle Kelp is the only aquatic instant kill.
 * On the Plants vs. Zombies website the Tangle Kelp is seen on land other than in the water.
 * In the Almanac entry of Tangle kelp, it says that it thinks Zombies cannot see him. This may be true due to the fact that Zombies never eat him, and Dolphin Riders keep on riding past when they would normally jump over.
 * Tangle Kelp 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: Ice-shroom, Lily Pad, Potato Mine, Threepeater, Doom-shroom, Jalapeno, Spikeweed, Torchwood, Tall-nut, Cactus and Blover.