Spellbook of cone of cold

Cone of cold is a medium-level attack spell. It is the Valkyrie's speciality spell.

Unskilled or basic
Same effect as a wand of cold. You will be prompted for a cardinal direction in which to cast the spell.

Skilled or expert
You may choose a location at which to cast explosions of cold. This location may be no more than 10 squares away, and must be in sight and open space. This spell cannot be used underwater or on the Plane of Water; if used while swallowed, it is automatically cast on your own location.

2 to 9 explosions follow; the first is centred at the location you chose, subsequent ones randomly at any of the nine squares around that point (unless swallowed). Each explosion affects the surrounding squares, as when unskilled/basic.

Any explosions that would be centred on yourself do not take place, but instead do damage as 'zap self' above.

Strategy
As detailed above, enhancing to expert skill gives no benefits over skilled for this spell.

The best possible casting scenario for this spell is if you are a level 30 knight with the Magic Mirror of Merlin, 18 intelligence, and are casting at a fire-resistant monster: you can cast up to 9 cold explosions, each of which could hit the monster's square for (6*17 + 3*17)*2 damage, for a total of 2754 damage. The total damage done across the whole casting area is up to 24,786. This makes this spell potentially the most devastating attack in the game, although under normal circumstances magic missile is likely to be better.

A level 30 valkyrie with a robe can cast this spell at 2% fail thanks to valkyries' speciality spell bonus. The fail rate is 33% if the valkyrie also wears gauntlets of power (more likely).