Attacks made with the Stone-Fire Dagger deal cold damage instead of piercing. If you score a critical hit with this weapon, the target must succeed on a Constitution saving throw (save DC 12) or be paralyzed until the end of its next turn, frozen in place and unable to move. If it succeeds, its movement speed is halved instead.
"At first, he thought the sudden chill was a simple, paralyzing fear of the dark.
Only then did he realize how wrong he was."