Having a discussion about Tether Essence, it says the targets share damage, does this mean include damage type? Target A takes 10 fire damage, Target B has fire immunity, do they also take the 10 damage? "When damage is dealt to one of them, the same damage is dealt to the other."
They take the same damage, amount, type, all that. Same.
— Dan Dillon (@Dan_Dillon_1) May 25, 2020
What seems to not be addressed here is order of operations.
“Take damage” and “deal damage” are, unfortunately, often used interchangeably, when in reality they describe two different things.
Dealing damage is -assigning- an amount damage to targets, without actually applying it yet. It’s a prediction of what the damage will be, assuming nothing else modifies that damage somehow.
Taking damage is the actual step of applying the final damage total, and actually reducing the amount of hit points a target has.
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So a basic example.
A wizard drops a Fireball on a group of enemies, rolls 8d6, and gets a roll of 33. For this example, let’s assume all enemies fail their Dexterity save.
That fireball then -deals- 33 fire damage to every enemy in the AoE. But that damage has not yet been applied. Hit points have not yet changed. First, each enemy must take the damage they’ve been dealt, and modify it.
An enemy with Fire Vulnerability is -dealt- 33 fire, but ultimately -takes- 66 fire damage. That’s how many hitpoints they actually lose.
An enemy who instead has Fire Resistance is -dealt- 33 fire damage, but ultimately only -takes- 16 fire damage. Again, that’s how many hitpoints they lose.
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So, what does that mean for Tether Essence? Well, the specific wording of the spell is that you copy the damage being -dealt-, not damage being taken.
If one person is hit by a fireball that deals 33 fire damage, the other person is also dealt 33 fire damage, even if they aren’t hit by the fireball.
If the first person has Fire Immunity, even though they ultimately -take- 0 damage, they have still been -dealt- 33 fire damage, meaning the second person also is -dealt- the exact same amount of damage, which they then have to modify.
They might end up taking 0 damage if they are also Immune to fire. Or they might take only 16 damage, if they have Resistance. Or they might take a whopping 66 damage, if they have Vulnerability. Et cetera.