Board Thread:General Discussion/@comment-17720232-20130326235912/@comment-4647769-20130404180146

If you activate an Ice-shroom between when the final wave of a level/Survival flagset comes out and the Ambush Zombies pop out of the pool covered in kelp, you won't have a problem with Ambush Zombies.

Ambush Zombies can only nibble on the front 4 plants of the lane if they're covered by Pumpkins, or the front 5 if the Fifth one has a Pumpkin. Blame the hitboxes.