Tangle Kelp

 Tangle Kelp is a single-use aquatic instant-kill plant, dragging any zombie down into the pool, but it can only kill one zombie. When it kills a zombie, it disappears. It is based on kelp, an aquatic algae with long, stringy leaves that have been known to tangle small fish.

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

Overview
Tangle Kelp is an aquatic plant. It kills the first zombie that comes into contact with it. After killing the zombie, it disappears to the water and it never comes out again.

Plant Food upgrade

 * Note: This is only for Plants vs. Zombies 2: It's About Time.

When given Plant Food, The Tangle Kelp will pull four random zombies underwater.

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

They also defeat 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 is wise to prepare backup plans for them just in case. The Squash makes a good backup alternative as it can eliminate multiple zombies if they are grouped closely enough.

General

 * The zombie that was pulled underwater by a Tangle Kelp does not die because the Snorkel Zombie's almanac entry states that zombies do not need to breathe.

Specific to Plants vs. Zombies

 * The Tangle Kelp and the Tall-nut are the only plants that the Dolphin Rider Zombie cannot jump over.
 * The Tangle Kelp, Spikeweed, Spikerock and Coffee Bean are the only plants that zombies will never attempt to eat.
 * 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, the Chomper, the Potato Mine, the Hypno-shroom and the Squash are the only instant-kill plants that are used on contact with the enemy.
 * The Tangle Kelp, the Chomper and the Squash are the only instant-kill plants that do not explode.
 * On the Plants vs. Zombies website, the Tangle Kelp is seen on land, instead of in the water.
 * In the Almanac entry for the Tangle Kelp, it says the Tangle Kelp thinks zombies and plants cannot see it. This may be true because zombies never attempt to eat Tangle Kelps and Dolphin Rider Zombies will attempt to ride past them instead of jumping 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 with the others being Ice-shroom, Lily Pad, Potato Mine, Threepeater, Doom-shroom, Jalapeno, Spikeweed, Torchwood, Tall-nut, Cactus and Blover.
 * The Tangle Kelp can be considered the aquatic version of the Potato Mine except it does not need time to arm and is not area of effect. However it costs the same amount of sun and has exactly the same recharge time.
 * In ZomBotany 2, one Tangle Kelp can kill a Tall-nut Zombie in one hit.
 * When tangling a Dolphin Rider Zombie, the player can actually see some leftover space where the zombie is supposed to be tangled, possibly because the Dolphin Rider Zombie is smaller than a normal zombie.
 * When an Imitater imitates a Tangle Kelp, the player can see that the part of the Tangle Kelp where it is on the water seems to be getting transparent, unlike the original Tangle Kelp.

Specific to Plants vs. Zombies 2: It's About Time

 * It now has seaweed surrounding itself instead of spiky vines.
 * Instead of wrapping itself around seaweed, it hides underwater.
 * Unlike the first game, its eyes have pupils.
 * This is the fourth plant in this game that went through a major redesign. The rest are Grave Buster, Spikeweed, and Starfruit.
 * The dirt can be seen after being planted.
 * Any zombie targeted by this plant will be stunned. This is clearly shown with Surfer Zombie.