Magic contamination is a potential side effect of powerful magic, divine wrath or favour, or the incompetent use of magic.
Various activities cause harmful magical energies to accumulate in your body. A small amount of magical contamination (a dark grey "Glow" status) is basically harmless, and will dissipate over time without any further effect. Larger amounts (5+ points) of accumulated magic contamination (a yellow, red, or dark red "Glow" status) will make you start to glow with magical energy; glowing is bad for two reasons.
- A glowing target is easier to hit.
- You may suffer damage and mutations from the magical energies your body has absorbed.
Your magic contamination level can be increased via the following methods. Any behaviour marked with (Z) offends Zin and will reduce the piety of his worshippers.
- Spending time under the influence of Haste while not berserk.
- +1 point for becoming hasted using a Haste spell or wand of hasting.
- +1 point for having your already-in-force Haste effect extended by:
- Rage extension (Z)
- A potion of haste or berserk rage (Z)
- Xom sending you berserk.
- Invoking Okawaru's Haste power
- +2 points for having your Haste extended by:
- The Haste spell or a wand of hasting. (Z)
- Spending time invisible.
- +1 point for making yourself invisible with a wand of invisibility or the Invisibility spell.(Z)
- +1 point for extending Might by:
- Quaffing a potion of might (Z)
- +1 point every time you successfully control a teleportation. (Z)
- +1 point every time you make a fully-controlled blink. (Z)
Miscasts and Miscast Effects
- Miscasting spells.
- Being struck by the Divinations miscast effect of Sif Muna's wrath.
- Unwielding a weapon with the distortion brand. (Z)
- The capriciousness of Xom inflicting a miscast effect on you.
- Zot traps (which apply random miscasts).
For purposes of the above, "spending time" under the influence of an effect means having that effect in force when the handle_time() function is called (roughly once every 20 turns). When this occurs:
- 60% chance of +1 contamination if you are invisible.
- 60% chance of +1 contamination if you are hasted and not berserk.
Base Contamination for Miscasts
To figure the baseline contamination level for a miscast, use the following calculation.
A= (spell_level ^ 2) * margin_of_failure B= A+250 C= B/500 With C being your final number. Fractional points are rounded randomly.
Contaminating Miscast Effects
The following miscasts can give you up to 18 contamination:
- Severity-3 Enchantments (25% chance)
- Severity-3 Translocations (25% chance)
- Severity-2 Transmutations (25% chance)
The following miscasts can give you up to 34 contamination:
- Severity-3 Transmutations (25% chance)
Dissipation of magic contamination is handled by the handle_time() function. Each time it is called:
- If you are neither Hasted (whether berserk or not) nor Invisible, you have a 50% chance of harmlessly dissipating one point of magic contamination.
- If you have 5 or more points of magic contamination, there is a 50% chance of a violent discharge occurring. The effects of this are as follows:
- If you are in a Sanctuary, there is a ((contamination + 1) × 4)% chance of being told that Zin has prevented a violent discharge of magical energies.
- If the previous check failed (either the random roll was too high, or you weren't in a sanctuary to begin with), then there is a ((total contamination + 1) × 4)% chance of some of your contamination discharging violently. When this occurs:
- If your contamination total is 10 or higher then there is a 50% chance of a magical explosion erupting from your body.
- You receive one mutation. 20% of the time this will be an entirely random mutation; the rest of the time it will be from the list of bad mutations. Mutation resistance applies as normal.
- A random amount of magic contamination (always at least one point, never more than 25% of your current contamination amount) is removed.
The magical explosions unleashed by violent discharge of magic contamination do damage specified by:
dice_def(3, you.magic_contamination × (you.is_undead ? 4 : 2) / 4)
For example, if you are not undead, and have 50 points of magical contamination (this is a really, really severe problem...), you will take 3d25 (3-75) points of physical damage (AC applies).
Antimagic and Contamination
Reading a scroll of vulnerability will harmlessly reduce your magic contamination by 1d5 points. This is a good reason to carry and save these rare scrolls, as their other effect, halving the MR of nearby monsters, is generally not that useful to most characters.
One of the aspects of Sif Muna's wrath is reducing the remaining duration of all your enchantments to 1 turn; when this occurs, your magic contamination level is also reduced by 1d5 points.
Also, quaffing a potion of cancellation will reduce your contamination level by 1-5 points, although whether one would want to waste such a rare potion solely for that effect is unsure.