After using the Ice Cage spell, at the start of the round, the strongest enemy hero is placed in an Ice Cage for x seconds. They will keep starting trapped until the opponent destroys the Ice Cage during the prep phase. The cage has 10 durability. At the end of prep phase, if the unit is still trapped inside the Ice Cage, they lose 5 of their Battle Prowess score.
To upgrade this spell, you will need Water Essence.