I made a countdown timer.

Mostly I brought it up because people keep suggesting anti-matter. Anti matter could be mistaken for a nuclear weapon, which could escalate to WWIII, so the wow means he can't use it anymore. A pure light pulse wont set off those warning systems. Or at least, not at the level I'm thinking of.

After 5 minutes of thinking about it, the only thing I could come up with concerns:

"HE IS HERE. THE ONE WHO WILL TEAR APART THE VERY STARS IN HEAVEN. HE IS HERE. HE IS THE END OF THE WORLD."

Bellatrix and Sirius are stars, and also Death Eaters. Voldemort has already torn apart Bellatrix to use the Dark Mark, and Harry can tear apart Sirius with the Partial Transfiguration trick people are talking about. How do we know Sirius is present? Because there is a Death Eater named "Mr Grim" who is stated to have known the Potters.

Hang on, isn't Sirius in Azkaban?

"I'm not serious, I'm not serious, I'm not serious..."

The "he" refers to both Tom Riddles, as they are branches of the same person.

Troubles with this suggestion:

The "HE IS THE END OF THE WORLD" part remains unresolved.

Narratively unsatisfying.

Warning for minor grossness: Harry can Transfigure bits of his body hair/skin into things, without appearing to move his wand. I don't currently see any particular use for this, but I wanted to mention it just in case.

So, like, is Snape in that crowd of Death Eaters, or what?

Harry kept wand and bag. Obviously planned. Especially with words suspiciously similar to prophecy.

Why the 'true form' with the weird appearance? Unless perhaps that form came about via sacrificial rituals and thus must contain evidence of such sacrifices to retain power.

What kind of sacrificial advantage do you get by destroying your nose forever?

If the mirror universe was antimatter, Harry would be annihilated instantly because his feet are touching the floor, even if the Cloak could shield everything else.

Couldn't he crawl?

Scientists of LessWrong, I have Important Questions for you:

What would happen if Harry donned his invisibility cloak and stepped through the mirror?

(Physics)

• Assuming CPT symmetry, Would the mirror universe be composed entirely of antimatter? Would the anti-nitrogen molecule annihilate with dust particles on Harry's cloak, emitting vast quantities of gamma rays?
• If so, would the cloak shield Harry from the gamma rays, or would they be "duplicated" the way visible light photons are? If the gamma rays are duplicated, the temperature of Harry would increase very rapidly. Does the invisibility cloak emit black body radiation? At what point would Harry be visible due to black body radiation alone?
• If Harry is not annihilate, what is the simplest experiment he could perform to take advantage of reverse-chiral weak interactions?
• Assuming the mirror permits electric fields to travel through it, what would the effects be near the surface of the mirror? Would electron on air molecules near the surface of the mirror be torn off and stick with their reflected positrons? Would the mirror become a giant capacitor? If so, how many coulombs of charge would it hold?

(Chemistry)

• Assuming the mirror universe is not composed of antimatter, what sorts of fun activities could Harry do with stereoisomers? For example, what schedule 1 drugs could Harry obtain on the cheap?

(Biology)

• Assume Harry starts eating in the mirror universe. What sorts of nutritional difficulties will he encounter? For example, would he be able to metabolize proteins? Carbohydrates? Fats? Nucleic acids? Are there any essential amino acids Harry will be missing?
• Would the mirror bacteria and fungi be able to metabolize Harry? Who would win in a fight: mirror bacteria or Harry's immune system?

It is said, in certain legends that may or may not be fabrications, that this Mirror reflects itself perfectly and therefore its existence is absolutely stable.

I take it "reflect" here means some kind of self-modeling aside from just optical reflection?

Wait a minute, aren't all human CEVs supposed to converge to roughly the same thing? (tell me if I've catastrophically misunderstood or misremembered the concept, it's been a while since I read the sequences)