In this world the thing is all about being frozen and getting unfrozen. There are a lot of new enemies to deal with and a few new plants get introduced to help thaw out any plants that need it.

Here is what you will unlock as you play through this world:

Hot Potato - Level 1 
Super useful in this world, just place it on top of a plant or enemy that is frozen to unfreeze it and the plant or zombie will be active again.

Pepper-pult - Level 7 
Another firey plant. Place this close to other plants and it will help keep the frost at bay for them. It is a decent long range weapon that could be a stable in this world.

Chard Guard - Level 12 
Place this plant in your front line to sling zombies backwards giving more time for your long range plants to destroy them.

Stunion - Level 20 
Useful and cheap plant which fires a cloud of gas at nearby zombies in the same lane stunning them.

Rotobaga - Level 27 
A reallt good, but often underused plant, this handy plant shoots zombies in four diagonal directions.