|"There are plenty of eye-witness accounts. Just because you're so narrow-minded you need to have everything shoved under your nose before you–"
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At least some content in this article is derived from information featured in Harry Potter: Hogwarts Mystery. Spoilers will be present within the article.
The Cursed ice was cursed by Dark Magic so that it would increase its own mass and thus spread throughout Hogwarts School of Witchcraft and Wizardry, encasing everything in its path in ice. It appeared to have had the ability to grow impervious to spells that were frequently used against it, and, according to the school's Matron, Poppy Pomfrey, believed that prolonged exposure could affect the mind of those who falls afoul of it and render their memories "erratic" and place them in some sort of delirium, which was the diagnosis she gave Ben Copper after he was found after having been trapped by the cursed ice.
At some point between 1 September, 1974 and 31 October, 1981, a student by the name of Jacob became intrigued with and began to search for the fabled Cursed Vaults, five secret rooms of ambiguous origins hidden somewhere inside the castle believed to contain ancient magical treasures older even than the school itself. Remembered by the school's Head of Herbology, Professor Sprout as a kind-hearted and thoughtful young man, and recalled to have been one of the best students of Filius Flitwick, the Charms Master. Though he successfully found, if not all at least some of them, his meddling accidentally unleashed a number of curses upon the school. Although Jacob successfully righted some of his wrongs by getting rid of the cursed ice that had been spreading throughout the school, he was still responsible for these breaches of the castle's security in the first place, not to mention therefore also to blame for all the injuries suffered by fellow students, leading to him being expelled.
1984-1985 school year
During this term, the cursed ice had showed up once more: This time in a room on the fifth floor corridor which, unbeknownst to most at the time, was located next door to one of the Cursed Vaults. Upon discovering this, the teaching staff successfully managed to keep it from spreading any further and securely sealed up the room afterwards. At some point during the semester, Severus Snape, the Potions Master, ordered Caretaker Argus Filch to guard it as to make sure people were kept out of the room, a task in which he was assisted by Mrs Norris.
Having overheard said conversation about the room with cursed ice, Jacob's younger sibling resolved to break in, hoping to find clues as to the location of the Cursed Vaults and by extension, their brother, who had ran away from home following his expulsion was remained missing ever since. Alongside some diligent, hard-working friends, said individual put Mrs Norris out of action by cleverly setting out a bowl of milk spiked with a Sleeping Draught for the cat to find and, as soon as it fell into a deep slumber, countered the barred door with an Unlocking Charm. Before the merry gathering could proceed into the room, however, they were caught off guard by fellow student Merula Snyde, who cast numerous knock-back jinxes against them before pushing past and rushing into the room herself, announcing her intention of finding the Vaults before any of them did.
Recognising the potential danger she was in, Jacob's sibling and his friends followed her: By the time they reached, the cursed ice, having already reacted to human presence in the room, had encased the Slytherin girl in ice, before the ice covering the floor grew all the way up to the roof, blocking the door through which they all entered. They all made it out of the room uninjured, however, although, as Professor McGonagall said the following year, it was uncertain what kind of damage had been done by their "ill-advised trip" into the room with the cursed ice, as it was known to have "strange effects on students".
1985-1986 school year
By the following school year, the ice had began to spread throughout the corridor outside of the locked room in which it had once been contained, which Minerva McGonagall, upon observing this, suspected it to be caused by a a chain reaction of sorts caused by someone having 'tampered with the Cursed Vaults". Though Gryffindor student Ben Copper had seemed fine when meeting with his Hufflepuff classmate Penny Haywood on the Hogwarts Express, he did not turn up for the Start-of-Term Feast, causing his friends and classmates to worry and suspect something to be wrong, with students and, once notified of his absence, staff, both starting to search for him. He was found by Professors McGonagall and Severus Snape in the same fifth floor corridor as the room that had been used to contain the cursed ice, although it was not so contained anymore, blocks of ice having spread across the hallway outside of it.
Almost immediately after, Jacob's sibling and Rowan entered the corridor: Having followed a series of clues left around the castle in the form of written notes from an unidentified individual signed with the initial of "R." that they believed would help them find out where their lost classmate. Taking cover behind a block of cursed ice as not to be seen by the professors and subsequently get in trouble for being there, and also as means to listening in on what the professors were saying. The Deputy Headmistress was somewhat alarmed to discover upon casting the Knockback Jinx to try and break free her student that, rather than shatter the ice as it normally did, it had no effect on it whatsoever. The ice, she deduced, had somehow come to be impervious to the spell. Severus Snape expressed annoyance over the absence of Professor Albus Dumbledore, who had left the school to look "for answers elsewhere", to which Professor McGonagall retorted that they did not require the Headmaster to get Ben Copper safely free from the ice. Ultimately, they successfully retrieved the frozen pupil by working together on melting the ice around him by the use of the Fire-making spell. With Ben Copper safe and knowing he would be taken to the Hospital Wing, Jacob's sibling and Rowan snuck back out, but fully intent on seeing Ben and get to the bottom of the mystery of his disappearance, and who R. was.
Shortly after Jacob's sibling and Rowan's failed attempt at entering one of the Cursed Vaults, ending with whatever curse safeguarded the entrance to injure and nearly killing the latter, putting him/her in a coma, Jacob's sibling overheard a fellow Second Year during Potion class mention that there now was cursed ice up in the Astronomy Tower, suggesting the cursed ice were still spreading, encasing all in its path. This was later confirmed by Rubeus Hagrid, from whom this individual learned the Astonomy professor were being trapped up there. By the end of the term, the situation had only gotten worse as the cursed ice continued to spread throughout the castle, turning whole rooms into crystalline prisons. When Jacob's sibling successfully broke the curse on the Ice Door leading into the vault itself into with some good help from fourth year student Bill Weasley in Gryffindor, and at least one of their other friends, the cursed ice disappeared instantly.