Crystal ball of seeing
|A magical device which allows one to see the layout of their surroundings. It requires a degree of magical ability to be used reliably; otherwise it can produce unpredictable and possibly harmful results.|
A crystal ball of seeing is an evocable item which, when used successfully, reveals a portion of the current floor around you, much like a scroll of magic mapping. It has no cost to use, but does have a high failure rate and may cause Divinations miscast effects when used incorrectly. Your Evocations skill determines both the likelihood of success and the spell power of the effect (and thus how much of the map it reveals).
When you evoke it, the game rolls 1d(6×Evocations). If it rolls:
1: 1 point of intelligence damage
2-4: Sets your MP to zero
5-9: You are confused for 10-20 turns
10-14: Nothing happens
15+: 50% chance of revealing part of the map
Spell Power: 50+1dEvocations
By the time your Evocations skill hits double-digits, you should be able to use it almost-reliably (though you are never completely safe from miscast effects). Even so, it's not the sort of item you'd be using in combat anyway, so it's mostly harmless to play with at lower skill levels. Possible uses for this include finding the stairs when trying to rush through a floor and hunting down vaults behind secret doors or locked inside of impenetrable walls.
Crystal balls of seeing were removed in 0.10.