Mercury Vapours

Version 0.31: This article may not be up to date for the latest stable release of Crawl.

Mercury Vapours
Level	2
School1	Air
School2	Alchemy
Source(s)	Book of Vapours Young Poisoner's Handbook
Casting noise	2
Spell noise	0
Power Cap	50
Range	3
Flags	Not self, Target

Briefly transmutes the air around a target into gaseous mercury, poisoning those who breathe it in. Further, the target and adjacent creatures (living or otherwise) may be weakened by mere exposure to the alchemical substance.

Mercury Vapours is a level 2 Alchemy/Air spell which causes smite-targeted poison on any non-resistant enemy within line of sight, then attempts to weaken enemies in a 3x3 area.

Alchemists start with this spell.

Useful Info

If the central target does not have poison resistance, it inflicts pow/25 (min. 1) poison "stacks" on it. If the target isn't poisoned, 1 extra poison stack is inflicted. Monsters can have up to 4 stacks of poison at a time. Stacks decay over time.

In addition, each monster in a 3x3 area (adjacent to, or on, the central target) has a 83% - (12 * HD) + (1.5 * power) chance

Higher stacks mean more damage per turn, according to the following table:

Average poison damage per 1.0 turn

# Stacks	Damage		Description
	Normal	rPois-
1	0.75	1.75	Poisoned
2	1	3	Very poisoned
3	1.25	4.25	Very poisoned
4	2.5	6.5	Extremely poisoned

Strategy

Mercury Vapours never misses, ignores AC, and is one of the few ways to inflict the weak status. It can be useful even if you aren't into Alchemy. The downside is that it relies on poison - damage is done over time, and cannot damage foes with poison resistance. These shouldn't be dealbreakers, however. You can kite susceptible enemies: apply a few stacks of poison, then retreat a few tiles, allowing the poison to do its job.

At low skill levels, Sting deals more damage/MP, but this spell is perfectly accurate and inflicts weak. In the early game, you may want to cast Mercury Vapours once per monster (to inflict weak and the extra poison), then use Sting. Once you gain more spell power, though, Mercury Vapours is more efficient, so feel free to forget Sting.

Tips & Tricks

• Ignite Poison is quite strong with any source of poison, including this spell. It converts poison stacks into instant damage, with a great increase in damage. The Ignite Poison + Mercury Vapours combo offers high reliability and MP efficiency for its level.
• In Tiles, you can count poison stacks by the number of green poison drops on the monster. 1 drop is 1 stack (poisoned), 2 drops is 2-3 stacks (very poisoned), and 3 drops is 4 stacks (extremely poisoned).

History

• Prior to 0.31, this spell was known as Poisonous Vapours. It was a level 2 Poison Magic/Air spell, had a range of 7, but did not have a chance to weaken foes. Also, it dealt power/15 stacks of poison, but with no bonus against non-poisoned foes.
• Prior to 0.27, Poisonous Vapours would create a short lived cloud, and wouldn't work if there was a cloud already there (including from the spell itself). Also, Vehumet did not consider this spell "destructive".
• Poisonous Vapours was added in 0.20.