Good questions. Let's take AK, since it's considered a Class A Death Curse in our cosmology. As I declare it, magic resistance is worth squat against it.
AK is one of the few curses with the ability to break
any magical defenses with the exception of the canon ones. A sacrificial shield born of love is the only true defense against it and it's a very complex spell that requires extremely specific conditions to activate. Otherwise, put up a shield? Poof. Ward your house? The curse breaks the ward, but the physical walls will block it.
The Egyptians' love for powerful warding magic is the primary reason for the Assyrians to develop the spell in the first place. Took five years, a thousand slave sacrifices and a
lot of luck to gain the knowledge to create it, first with arithmancy and runes, and then as the green ray of death we all know and hate.
And very few people know about the special countermeasure, mostly because it's a sacrifice and one does not simply come back from the dead. More people know about the Horcrux/phylactery defense, and that's a perfectly valid defense because it's still technically a sacrifice. Either of someone else to make the horcrux or a sacrifice of sanity, light, goodness, etc. for the other kinds.
Sacrificial magic is incredibly OP if the conditions are ripe.
Tl;dr: Lily Potter was a bloody Charms genius. Don't
ever get hit by AK.
Now, I've said that there's no magical defense against the AK, but that's the operative words.
Magical defense.
There are other
types of defenses. One is of course, a physical defense. A Keyblade will block it. A lightsaber will block it, but that's solely because it's a solid bar of light/plasma. A ME Kinetic Shield or those Gungan/Naboo shields will work. A Dresden magical KE shield won't work because it's still powered by magic. A hull will work. Basically, it has to be a solid physical defense or technological shield. However, if it's a shield that specifically blocks energy attacks, it will fail. Weird? Yeah. That's magic for you.
On armor: Clothes obviously don't help. A suit of armor worn on the body won't help. Too many openings for the energy to get through. A suit of armor that acts as a physical defense will block it. That tells you that you need something thick to defend you, so basically, the only physical armor that can protect you is power armor and good-quality, well-tended ones at that. Dorn's power armor will work fine as such, but a headshot or a shot that goes through an unprotected hole will render him dead anyway.
A beam/bolt of magic, bullet or blaster/lasgun bolt will also deflect the spell, but you basically have to be a sharpshooter to get it before it gets you, so they're not reliable as defenses.
The second type of defense is immortality. If you die, but your nature allows you to return to life, then you're fine. The AK works, yet it doesn't stick. That's why phoenixes can be used as shields against AK. They aren't strictly speaking immune. Death simply doesn't stick for them. Vampires, naturally, have this type of immunity. There are other things out there with the immunity as well.
That said, resurrection spells and items are the one thing we have that Harry Potter doesn't have that will make this problem little more than a speedbump. Jury's still out on how long you can stay dead before even a resurrection item/spell will fail, so don't act like you can simply walk through Death's door like it's a revolving one.
The third type of defense is a spirit. You're already dead or you were created spontaneously out of the aether, so why would it affect you? Spirits will by and large block it. Ghost Pokémon will Faint. Ghost Digimon will absorb it. Some spirits might actually absorb or have AK go through them. Check your local spirit or loa to be sure you have the right type of spirit to block AK, or else you'll have a
very short surprise.
The fourth type of defense that would work is, well, pretty obvious. Divinity. A divine shield or essence will block it, full stop and even the weakest god can block it. Not even an AK cast by a god will do much more than a nosebleed,
unless it's a death god like Hades or Anubis or the Overgod of All Things aka God/Morgan Freeman/Eru Illuvatar/Yahweh/Allah/etc casting it. For the purposes of this discussion, eldritch physiology counts as divinity. Some demigods will be immune. Some won't. And they will never know until they've been hit so even being a demigod isn't reliable.
And for
@Krein's benefit, the NAOH!God is NOT the same as the SMT!Yahweh. He's also above Deus in the divine pecking order.
Anyway, the LOLNOPE T-shirts and assorted shields are interwoven with spiritual/divine essence. That's how they can block the AK. But it's only for a limited time and you'll need a god or powerful spirit to pour their essence into them to make them anew.
So tl;dr, throwing rocks, magic bolts, bullets, phoenixes, Franklin Badges, LOLNOPE Shirts (thrice cursed and done), Gengars, Bakemon, Liches, zombies,
@Blackout,
@SailorMidgard,
@Citrakite,
@Omanisat with power armor,
@SlugSLinger,
@Krein,
@Whatmesage and
@Necron_Lord in the path of an AK are all perfectly valid defenses if you don't have the knowledge to use the Sacrificial Spell which will render the target immune in exchange for your life. However, they might not like you very much afterwards.
The fifth and final defense is a good offense. Shoot the bastards before they shoot you and you'll have no problems.
Other death curses, however, will have other effects and will affect these defenses differently, so don't think one defense will necessarily work on another curse. The AK is just the most well-known one and the easiest of the A-class death curses to cast.
Quite possible in this universe. Will almost certainly be vulnerable to holy energy, though.
Genetically speaking, a great portion of current humanity would have this spark of lineage. Same reason Charlemange would have a lineage in the millions: time.
The time is so long since Aragon's days that technically, any one of us mere humans can be a candidate. Mystically speaking, I could work with it.
Be funny if it meant some private from a third-world nation manages to head-shot you with a simple rifle. Never has irony been so great when someone so high is brought down by someone so low.
