Absolute Zero

 is the final upgrade of path 2 for the Ice Tower. It costs $1700 on Easy, $2000 on Medium and $2160 on Hard. Upgrading to Absolute Zero unlocks the Absolute Zero Ability; when used, it will freeze the entire screen of bloons for 4 seconds (including White Bloons and Zebra Bloons). It does not affect any M.O.A.B. Class Bloons. It takes approximately 30 seconds to recharge this ability on Fast Forward. 

Trivia

 * This is the only upgrade for the Ice Tower that does not have an animated element to it's appearance on the track.
 * Absolute Zero is the cheapest Special Ability in Bloons TD 5,the 2nd one being Sabotage Supply Lines.
 * Absolute Zero Ability can freeze White Bloons, Zebra Bloons, and Camo Bloons.
 * In Bloons TD 5 iOS, Absolute Zero can freeze and slow M.O.A.B. class bloons if the ability is used.
 * Absolute Zero in real life is -459.67 degrees F and -273.15 degrees C.