Pestilent Chant

The characters research into forbidden magic unearthed sickening secrets, that allow the caster to chant in an unknown, esoteric language while casting spells. Their Constitution is increased by 1 and they gain the following benefits:

• When casting a Ritual spell or a spell that takes more than 1 minute to cast, the caster can sheathe his physical form in a 10 foot aura of sickening mist centered on him. This aura lasts for 1 hour. If a creature ends its turn within that aura it has to make a Constitution Saving Throw against the casters Spell Save DC or become poisoned until the end of their next turn
• When casting a Spell that deals damage, the caster may sheathe their magic in poisonous fumes. The character may change up to half the damage dice of the spell rounded up to deal poison damage
• The first time the character suffers poison damage after a long rest, instead of suffering damage, the character instead gains that many temporary hit points