Mercury Vapours

Version 0.30: 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.

Poisonous Vapours is a level 2 Poison/Air spell which causes smite-targeted poison on any vulnerable enemy within line of sight.

Venom Mages start with this spell.

Useful Info

Poisonous Vapours inflicts pow/15 (min. 1) poison "stacks" on a single target. Monsters can have up to 4 stacks of poison at a time. It does nothing against foes with poison resistance.

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

Poison stacks will decay as turns pass.

Strategy

Poisonous Vapours is a good spell to pick up, even if you aren't a Venom Mage. It is a level 2, smite-targeted spell, which never misses, ignores AC, and deals good damage (for its level).

The downside of the spell is that it's poison - damage is done over time, and it does nothing against foes with poison resistance. But these shouldn't be dealbreakers. You can kite susceptible enemies: apply a few stacks of poison, then retreat a few tiles, allowing the poison to do its job.

Ignite Poison

With Ignite Poison, Poisonous Vapours jumps from "good" to "excellent". Ignite Poison converts poison into immediate damage, with a bonus multiplier of 200% to 300%. This combination is cheap and extremely strong, much stronger than what a level 3 spell would suggest.

At ~30 power, casting Vapours x2 -> Ignite Poison deals 8d13 damage (avg. 56) - for reference, Iron Shot at 70 power deals 9d7 damage (avg. 36), and Plasma Beam deals 2d53 (avg. 54). While this combo is poor at turn economy (3 turns to cast), it's good to put things into perspective. Poisonous Vapours has better range, is more reliable (ignores EV and AC), and it's a level 3 spell. Has the added benefit of Olgreb's Toxic Radiance, which is great against crowds.

Overall, it's a viable combo into Vaults, Depths, and even Zot (provided you have another way of killing resistant enemies). In Zot, many targets are vulnerable to poison, including moths of wrath, non-green draconians, quicksilver dragons, and orb guardians.

Tips & Tricks

• Low-XL Venom Mages may want to use Sting for the reduced MP cost. Otherwise, Poisonous Vapours is almost a direct upgrade; it's more accurate and has better range. Note that Sting deals some damage against poison resistant foes, so you'll want to keep it around for a bit.
• 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 0.27, 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.