A Frozen unit has limited capabilities, due to being so cold. Each combat round, they accrue 2d6 (2 to 12) Cold Fatigue. They're also slower to attack than other units, and they suffer a significant penalty to Attack Skill and Defence Skill.

Cold Attacks cause freezing. The chance of being frozen is presumably the same chance of being burned; 4% per point of damage after the Damage roll but before the Protection roll, divided by 3 for Cold Fatigue. 10 Cold Resistance makes a unit immune; other sources of immunity include having a Heat Aura or being an Ethereal Spiritform.

Water magic has a couple of spells dedicated to freezing, including the Freeze spell.

There are "Encase in Ice" spells, which are better at immobilizing targets but inflict less fatigue, but these may only be used underwater.

A Frozen unit will eventually thaw; there's a base 25% chance each turn, plus 5% for each point of Heat on the Scales, plus 1% for each point of Cold Resistance. Cold is considered negative Heat, while an Elemental Vulnerability is considered a negative Resistance.