Undertow

Difficulty: Easy-medium

Undertow is an achievement in Plants vs. Zombies 2: It's About Time. It requires the player to kill ten zombies with Tangle Kelps, and it is worth 1,000 XP on Android devices and 10 points for iOS devices in Game Center.

Strategies
Play Big Wave Beach - Day 5 because you can get a lot of Tangle Kelps in that level. But try to focus on strong zombies too. You can also try feeding the Plant Food on Tangle Kelp again and again which is real easy. The easiest way to get the achievement is by using Plant Food on Tangle Kelp. Otherwise, boosting it makes it more efficient.