Ice-shroom

The Ice-shroom can freeze all the zombies on the screen for a few seconds, then slows them down.

Usage
Single use, to activate it just drop it in any empty spot or Flower Pot on the screen. After a second, the Ice-shroom will freeze every zombie on the screen (including and/or Dr. Zomboss, but not counting, which can't be frozen, Dolphin Zombies (though not their riders) and  with Pogo Sticks, as they will slow down but not stop completely) and do a slight amount of damage to each one. Zombies will unfreeze after a couple of seconds, but then will be slowed for a few more seconds.

Suburban Almanac Entry
Ice-shroom

Ice-shrooms temporarily immobilize all zombies on the screen.

Damage: very light, immobilizes zombies.

Range: all zombies on the screen

Usage: single use, instant

Sleeps during the day

Ice-shroom frowns, not because he's unhappy or because he disapproves, but because of a childhood injury that left his facial nerves paralyzed.

Cost: 75

Recharge: very slow

Standard Levels
Plant the Ice-shroom when tough zombies (like the Gargantuar) are trying to eat your other plants. Against Dr. Zomboss, the Ice-shroom can be used to destroy fireballs, and also to freeze him so he can be damaged for more seconds at a time.

Whack-a-Zombie mini-game
Use the Ice-shroom when you need a little extra time to whack a large wave of zombies. If you have enough Sun, you can take that time to drop a Grave Buster at the same time.