Freezing

Weapons with the freezing brand will glow with a cold, blue light when wielded (this identifies it) and will freeze monsters when it hits them, causing more damage to monsters without cold resistance, and even more to monsters who are vulnerable to cold. It will also temporarily slow cold-blooded monsters not resistant to cold.

Weapons can be temporarily enchanted with the freezing brand with the level 2 spell Freezing Aura.

Tips & Tricks

This brand is best on a high-damage weapon, since the damage is multiplicative. It is the best general-purpose brand, since very few monsters are entirely immune to cold, and it has the useful secondary effect of slowing a number of monsters, including the draconian packs in Zot. Frost giants are usually generated with freezing-branded weapons.

Added damage:

• Not cold resistant or susceptible:
  • +25% damage on avg.
• Cold resistant (1 or 2 levels):
  • +12.5% damage on avg.
• Cold resistant (3 levels):
  • +0 damage
• Amount of damage is reflected by punctuation at the end of message:
  • 1-2 "You freeze ... ."
  • 3-6 "You freeze ... !"
  • 7 and more "You freeze ... !!"

Source:http://www.crawl.webpark.pl/melee.html

The extra damage ignores AC. Also note that some particularly dangerous monsters are cold-blooded, including the Lernaean hydra and draconians.