Enhanced Freeze is the first upgrade on path 1 for the Ice Tower in BTD5. It increases tower's range and the time bloons are frozen for from 1.43 seconds to 2 seconds. It costs: $190 (Easy), $230 (Medium), $245 (Hard), and $270 on (Impoppable). In BTD5, it changes the tower's appearance so that the 'stone' it stands on is now blue.
In BTD6, this upgrade returns as the first upgrade of Path 2. Instead of increasing the Ice Monkey's range, it increases the attack speed of the Ice Monkey by 33% (from per 2.4 seconds to per 1.8 seconds). Like similar upgrades in the past, it still increases the frozen duration from 1.5 seconds to 2.2. The bloon freeze duration increase remains similar across both games. Increasing radial size of Ice Monkey can only be obtained via the Larger Radius upgrade (besides Snowstorm and Absolute Zero). It costs $190 on Easy, $225 on Medium, $245 on Hard and $270 on Impoppable. In BTD6, the upgrade visual adds a pair of red earmuffs.