Death's own cloak
The cloak has always seemed the odd Hallow out. It makes you invisible, but no more invisible than any other invisibility cloak. Dumbledore said vaguely that the cloak could "protect" anyone under it, but we see that you can easily be Petrified while under the cloak, and so presumably other curses won't have any trouble getting through either. Its only other special power seems to be not getting weaker over time. How can that measure up next to a super-powerful, semi-sapient want and a stone that (seemingly) lets you talk to dead people?
I finally realized that there's one power the cloak might well have, which would fit in seamlessly with everything JKR set up for it. It's just that the characters never had occasion to test it.
While I have plenty of objections to the context of Harry walking up to commit suicide by dark lord, if he had ended up there by other means (like, having had the opportunity to try other means of getting the Horcrux out of his forehead and this actually being the last option, or at least realizing he'd been robbed of the chance to try other things and holding it against Dumbledore), it would be a powerful moment: with the fairy-tale resonance previously set up that one removes the cloak in order to face death not as a victim but an equal, Harry takes off the cloak that hides him from death and faces Voldemort's killing curse.
Metaphors are frequently literal in the Potterverse: depression is a spooky cloaked figure lurking about trying to suck your soul out, fear is a monster in the closet, luck comes in a bottle.
What about Death? Dumbledore's vague "protection" gets everyone thinking about a cloak that shields one from harm generally, but maybe that's stretching the tale too far. Beedle didn't say the cloak hid the youngest brother from Death, his brother Grievous Bodily Harm, and their cousin Ouch That Stings: it hid him from Death, and only Death.
What if the cloak can block Avada Kedavra?
That would mean that in taking off the cloak, Harry was literally removing his protection from death - and specifically, a means of death he'd faced and escaped before.
It might protect against other normally fatal actions, too. Perhaps if Harry had put his cloak on in the DoM, he could have walked through the Veil and then walked right back out again. Maybe even with Sirius, if he popped Sirius under the cloak first.
How the cloak manages to shield one from death but not injury, I can't say, though developing oddly specific magic doesn't seem out of character for wizards. Maybe the anti-death property, whatever it is, interferes with any shield charms.
Just for fun, though, here's one possibility: interwoven with the usual demiguise hair are threads from the Veil, or something like it. Being enveloped in something with just a little bit of whatever the Veil is removes your "death" (life force? soul? who knows?) from the world, at least in part; that is, your "death" is already behind the Veil (but anchored to your living body), and so anything that would ordinarily cause your death can't reach it. But since only your death is out of reach, not the rest of you, everything else still touches you as usual.
This could explain why the cloak's power never fades: the demiguise hair (being dead and so probably having some interesting reaction to Veil threads) is affected by being part here and part beyond the Veil, and so time doesn't pass for it as normal. It could also explain a property some here have speculated it also has, that of making a frequent wearer feel "cut off" from the world: you actually aren't all here. (It wasn't designed as a trap, but why would you expect Death's own cloak to have no side-effects for mortals for whom it was not designed, after all?)
If any of the characters had ever figured out this property of the cloak, we might have had some very interesting adventures behind the Veil, and who knows what else.
If I'm right, it would also mean that, had James had the cloak that Halloween night, there is a very slight chance he could have lived long enough, before Voldemort realized the problem and tried a different spell, to give Lily enough precious seconds to grab Harry and jump out the window while Apparating away. Oops. Dumbledore can console himself with the thought that if James was careless enough not to have his wand on him, he no doubt would not have had the cloak to hand either, surely...
I finally realized that there's one power the cloak might well have, which would fit in seamlessly with everything JKR set up for it. It's just that the characters never had occasion to test it.
While I have plenty of objections to the context of Harry walking up to commit suicide by dark lord, if he had ended up there by other means (like, having had the opportunity to try other means of getting the Horcrux out of his forehead and this actually being the last option, or at least realizing he'd been robbed of the chance to try other things and holding it against Dumbledore), it would be a powerful moment: with the fairy-tale resonance previously set up that one removes the cloak in order to face death not as a victim but an equal, Harry takes off the cloak that hides him from death and faces Voldemort's killing curse.
Metaphors are frequently literal in the Potterverse: depression is a spooky cloaked figure lurking about trying to suck your soul out, fear is a monster in the closet, luck comes in a bottle.
What about Death? Dumbledore's vague "protection" gets everyone thinking about a cloak that shields one from harm generally, but maybe that's stretching the tale too far. Beedle didn't say the cloak hid the youngest brother from Death, his brother Grievous Bodily Harm, and their cousin Ouch That Stings: it hid him from Death, and only Death.
What if the cloak can block Avada Kedavra?
That would mean that in taking off the cloak, Harry was literally removing his protection from death - and specifically, a means of death he'd faced and escaped before.
It might protect against other normally fatal actions, too. Perhaps if Harry had put his cloak on in the DoM, he could have walked through the Veil and then walked right back out again. Maybe even with Sirius, if he popped Sirius under the cloak first.
How the cloak manages to shield one from death but not injury, I can't say, though developing oddly specific magic doesn't seem out of character for wizards. Maybe the anti-death property, whatever it is, interferes with any shield charms.
Just for fun, though, here's one possibility: interwoven with the usual demiguise hair are threads from the Veil, or something like it. Being enveloped in something with just a little bit of whatever the Veil is removes your "death" (life force? soul? who knows?) from the world, at least in part; that is, your "death" is already behind the Veil (but anchored to your living body), and so anything that would ordinarily cause your death can't reach it. But since only your death is out of reach, not the rest of you, everything else still touches you as usual.
This could explain why the cloak's power never fades: the demiguise hair (being dead and so probably having some interesting reaction to Veil threads) is affected by being part here and part beyond the Veil, and so time doesn't pass for it as normal. It could also explain a property some here have speculated it also has, that of making a frequent wearer feel "cut off" from the world: you actually aren't all here. (It wasn't designed as a trap, but why would you expect Death's own cloak to have no side-effects for mortals for whom it was not designed, after all?)
If any of the characters had ever figured out this property of the cloak, we might have had some very interesting adventures behind the Veil, and who knows what else.
If I'm right, it would also mean that, had James had the cloak that Halloween night, there is a very slight chance he could have lived long enough, before Voldemort realized the problem and tried a different spell, to give Lily enough precious seconds to grab Harry and jump out the window while Apparating away. Oops. Dumbledore can console himself with the thought that if James was careless enough not to have his wand on him, he no doubt would not have had the cloak to hand either, surely...