NCF – Extended list of Neutral creatures.

Many already have immunity to deadly cold, but the cave demon's blade, spirit ability, or crossbow shot or running attack SHOULD take them down; otherwise, it will be impossible – crystalline scales will definitely be unnecessary.

Crystalline scales only work on direct kill abilities – deadly cold, crippling grip, cleaving sword. A crossbow shot or running attack is irrelevant here (there is no direct kill, only increased damage (attack) through defense reduction).