The most advanced way to deal with Fiendfyre was Annihilation Magic. Unfortunately, Tris did not know it.
Next came high-level ending magic such as the Thousand Knots' End Curse. Tris did know that one, but in actual combat, his chances of suppressing Voldemort's Fiendfyre alone were about the same as a meteor falling from the sky right now and crushing Voldemort to death.
Was a meteor falling from the sky right now?
No.
So Tris could not suppress it alone, either.
The Mirror Seal was a very unusual sealing technique. The Mirror World was rather different from the Shadow Realm. Both were constructed from magical power, but their structures were completely different.
Calling it stable was a stretch: a simple fluctuation of magical power could break it, and any wizard over fifteen could master that.
Yet calling it unstable was not quite right, either. If you did not know the trick and could not use mirror magic, once you were sealed inside, you would probably have to wait until the spell itself ran out of magical power before you could escape.
Almost no other magic had any effect on the Mirror World.
Tris used a Freezing Spell to create a mirror surface on the ground, then sealed the Fiendfyre inside, cutting its connection to Voldemort. With no magical power sustaining it and no material to burn, the Fiendfyre vanished completely in an instant.
After pulling that off, even Tris himself felt he had been almost indescribably cool.
Voldemort was genuinely taken aback this time.
He did not understand mirror magic and had never encountered it before.
It had been particularly popular around the time of his birth, but by the time he began learning magic, the spread of magical fluctuation techniques had left it utterly neglected.
Knowing its enormous weakness,