Improved Ice Tower

 is the first upgrade for the Ice Tower in BTD4. It increases the time bloons are frozen for, and increases the Ice Tower's attack radius. It costs $190 on Easy, $225 on Medium, $245 on Hard.

Trivia

 * This upgrade combines Longer Freeze and Wide Freeze Radius, upgrades from earlier BTD games.
 * It was later renamed to Enhanced Freeze in BTD5.