Neither, you just have resistance (1/2 damage). Resistance and vulnerability are like advantage and disadvantage, you either have them or you don't, and if you have both they just cancel each other out.
There are certain other spells and effects which explicitly cause you to "take half damage from" certain sorts of damage or attacks, or cause enemies to "deal half damage" with those sorts of attacks, without using the word "resistance." You can stack resistance plus a "take half damage from" sort of thing to end up with 1/4 damage, but still no total invulnerability.
Resistance and vulnerability are like advantage and disadvantage, you either have them or you don't, and if you have both they just cancel each other out.
Not strictly true about having both. The Damage Resistance and Vulnerability rules say you apply resistances first and then apply vulnerability. It creates this weird situation where odd damage gets 1 damage removed because of rounding down when halving due to resistances.
Resistance and then vulnerability are applied after all other modifiers to damage.
I don't know anyone who actually does it that way because it's stupid (it should cancel out like Adv/Disadv) - but that's RAW.
If I have resistance to piercing from rage and a magical effect that grants resistance to piercing do I get Immunity or do i just take 1/4 Damage
Neither, you just have resistance (1/2 damage). Resistance and vulnerability are like advantage and disadvantage, you either have them or you don't, and if you have both they just cancel each other out.
There are certain other spells and effects which explicitly cause you to "take half damage from" certain sorts of damage or attacks, or cause enemies to "deal half damage" with those sorts of attacks, without using the word "resistance." You can stack resistance plus a "take half damage from" sort of thing to end up with 1/4 damage, but still no total invulnerability.
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I'm going to make this way harder than it needs to be.
Not strictly true about having both. The Damage Resistance and Vulnerability rules say you apply resistances first and then apply vulnerability. It creates this weird situation where odd damage gets 1 damage removed because of rounding down when halving due to resistances.
I don't know anyone who actually does it that way because it's stupid (it should cancel out like Adv/Disadv) - but that's RAW.
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Excellent catch on the detail there !!
But, yeah, nobody is going to do it that way because it's silly.
Well, except for the example in the book explicitly does it so I wouldn't be so sure.