What ways are there for a PC to negate poison damage resistance or immunity from an enemy?

Question

For example; a player has time to prepare before a fight with a creature that is resistant or immune to poison.

Are there ways to negate poison resistance or immunity? (Even temporarily by magic, an item, or other means)

Of course it’s possible to avoid their special resistances by utilizing a weapon with a different damage type, but I am wondering about ways a PC could negate them instead.

(Answer should be based on officially published content only)

Answer 1

You have a few good options against resistance, but immunity is harder to overcome

Against resistance, you have a few spells that can be used to give vulnerability to poison to creature. They are:

• hallow (Energy Vulnerability)
• contagion (Flesh Rot)

At the DM's fiat, you may also use bestow curse to negate a creature's resistance to poison damage.

Introduced in Tasha's Cauldron to Everything, the new Poisoner feat allows you to ignore resistance to poison damage when dealing poison damage.

From class features, your only choice is Grave Domain's Channel Divinity: Path to the Grave.

Against immunity, your best option is to use polymorph (or true polymorph) on your target into a creature that doesn't have resistance nor immunity to poison damage. The target, however, will return to its original form upon reaching 0 hit points, which doesn't help much.