Immunity...

[HelixIconix]

Does immunity to a damage type reduce damage to 0?
Or perhaps, does immunity to a damage type mean that such a creature "takes the damage", but loses no hit points?
For example, let's say a creature is immune to necrotic damage by way of its stat block, and by way of a feature from a different source (class, magic item, template) has the ability to deal half of the necrotic damage they take to another creature within their reach.
Would the damage (let's say 14) of an incoming effect be reduced to 0, and half that be 0 dealt to the other creature?
Or would that damage be ignored by the immunity and remain at its full value, therefore dealing 7 damage to the other creature?

[Keravath]

Just my opinion but if the ability is worded as :

"ability to deal half of the necrotic damage they take"

and the creature is immune to necrotic damage then I would say that the damage they take is zero due to the immunity and the amount they could inflict on another creature is also zero.

In a similar way, if a cleric cast warding bond on a yuan-ti and the yuan-ti was hit with poison damage ... the warding bond spell says
"Also, each time it takes damage, you take the same amount of damage."

Since the yuan-ti takes no damage from poison, the cleric would also take no damage if the yuan-ti is hit by a poison attack.

[Snownine]

Do you happen to have any exact wordings of the effects you are referring to? It might make it easier to determine the most logical interpretation.