Poisoning magic itself is not an exercise for the faint of heart, but Venomancers are willing to put in the effort to do so. These wizardly toxin specialists can infuse their own spells with harmful compounds, giving their magic a potent boost, but their most feared ability is possessed by some of the more accomplished among their number: the ability to poison the magic of other spellcasters, turning their own power against them.
Beginning at 2nd level when you take this archetype, you learn to safely harvest and handle toxins. You gain proficiency with the poisoner’s kit and on a failed check, you are not poisoned, though you still do not collect any poison.
You also have some low-level, permanent wards against poisonous effects. You have advantage on saving throws against spells and effects that would deal poison or necrotic damage to you.
Finally, spells on the Poison list always count as wizard spells for you, and you may copy a spell on the Poison list into your spellbook at the normal cost for a spell of that level, though other wizards cannot also copy them from your spellbook unless it is normally on the wizard spell list.
At 6th level, you learn to infuse your spells with poison. As part of casting a spell, you may poison the magic of the spell. This requires a dose of advanced poison as an additional material component. For a spell that requires a saving throw, if a creature fails its saving throw, it takes an additional 2d6 points of poison damage and is Poisoned for one minute. If the spell requires an attack roll, on a hit the target takes an additional 2d6 points of damage. If the spell transports you from one place to another, you leave a cloud of poisonous vapor that persists for one minute behind in your starting square. A creature that starts their turn in that space or enters it must make a Constitution save against your spell save DC, taking 2d6 points of poison damage and becoming Poisoned for a minute on a failed save. A creature that succeeds on its save takes half damage and is not Poisoned. A creature suffering the Poisoned condition from this ability may make a Constitution save against your spell save DC at the end of each of its turns, ending the condition on a success. Once you have used this ability a number of times equal to your proficiency bonus, you can’t do so again until you finish a long rest.
At 10th level, you learn to poison the magic of others, harming them and disrupting their spells. You learn counterspell if you do not already know it. When you cast counterspell, if you successfully disrupt a spell, you may also spend a dose of advanced poison as an optional material component to deal 3d6 poison damage to the creature whose spell you disrupted and it cannot attempt to cast a different spell.
Beginning at 14th level, whenever you would deal acid, necrotic, poison, or psychic damage, you can choose to deal acid, necrotic, poison, or psychic damage instead. You also become immune to poison damage and the Poisoned condition.
Also at 14th level, your ability to infuse poison into your spells improves. When you cast a spell with a single target, you may expend a dose of any poison (common or named). If the target is struck by a spell requiring an attack roll or fails its save against a spell requiring a saving throw, it is also subjected to the effects of the poison. If the poison’s save DC is lower than your spell save DC, it increases to match your spell save DC. Once you have used this ability, you can’t do so again until you finish a short or long rest.