Surprise attacks

Ambush Zombies are when zombies suddenly appear in a stage. This happens in all of the stages except for day. The ambush zombies can also be referred to as Ambush Zombies and usually come in sets of three; They emerge from graves at night, emerge from the pool in the Pool and Fog levels, and are dropped down by Bungee Zombies on the roof. (Night levels are the exception of the "come in sets of three" principle, as there are always more than three graves.) The Ambush Zombies can be normal zombies, Conehead Zombies, Buckethead Zombies, and their Ducky Tube Zombie forms.

Strategies

 * For Night Ambush Zombies, just use Grave Busters to destroy the graves before the final wave.
 * For Pool and Fog Ambush Zombies, when playing to the final wave, use an Ice-shroom right after the wave comes but before the Ambush Zombies pop up from the pool. This takes extremely good timing, but can stop the Ambush Zombies from ever emerging. If you can't get the hang of this, another way to deal with them is to plant Explosive Plants in the middle of the Ambush Zombies.
 * For Roof Ambush Zombies, Umbrella Leaves will repel the Bungee Zombies trying to place them down, preventing the zombies from entering play.

Trivia

 * Ambush Zombies in Pool and Fog levels have seaweed on them.
 * The seaweed patterns are always random.
 * It is exactly unknown how the ambush zombies from pool or fog levels have seaweed on them. It is possible the pool could have algae in it, but that still won't explain the green clumps.
 * Maybe the seaweed could have came from the Tangle Kelp when they were pulled down, but the seaweed appeared before Tangle Kelp was unlocked, and still appears even if no Tangle Kelp was used in the current level.
 * Ambush Zombies have three mini-games featuring them: Grave Danger (which is a hidden Mini-game), Whack a Zombie, and Bungee Blitz (which is also a hidden Mini-game).
 * It is also unknown how the zombies got there in the first place.
 * Maybe they got stuck in there while you fought them in Day and Night.
 * The Day levels are the only levels that don't have any surprise attacks.
 * In 3-1, 3-2, 4-1, 4-2, 5-1, and 5-2, there are only two Ambush Zombies instead of the normal three.
 * In ZomBotany 2, there are no Ambush Zombies