The Ice Sword

The blacksmith had one job: to make this sword last billions of years, and also be the best sword he'd ever made. And making it be his best... now, that was going to be a challenge. He'd already made several swords of legend, known for their tendency to not get damaged, last thousands of years, and more. Some of them had stronger magical powers than the resistance to damage, but they were all purely cosmetic. This sword, however... it would have an ability capable of destroying mountains, killing armies within a minute, and more. It was all made possible by the wizard standing next to the blacksmith, streaming magic into the raw metal. The blacksmith knew that he didn't have long to get the blade done. In fact, the deadline was midnight that night. It was noon.

Thousands of years later, a brave adventurer stepped into a room, deep within a floating island. Floating in the center of the room was a sword. It wasn't any ordinary sword you could buy off a weapon merchant, or even pay a blacksmith to make for you. No, the smith who had made this was long dead, the secrets to making these gone with him.

When the Ice Sword touches anything, as long as the wielder has at least a small amount of magical power and is actively streaming power into the sword, it will turn whatever it touches to ice. Abuse of this power has been long debated, such as having a highly skilled swordfighter wield it, and someone else streaming into it, or shooting ice bolts, but seeing as nobody knows where the sword is, none of the theories have been tested.
The Ice Sword is also basically indestructible.
Other than it's magical powers, the Ice Sword is a really nice longsword. The blade is slightly longer than average, but the whole sword is lighter. It has a slightly blue tint to the blade, and the rest of it seems to be made of ice, but it's actually just really good illusion magic.

Mechanics & Inner Workings

When taken into an anti-magic zone, or when a counterspell is cast on it, all magic on it stops working, including the invulnerability and the hilt illusion. It takes exactly fifteen minutes for the sword to reboot the magic after the counterspell is cast/it's taken out of the anti-magic zone.

Rarity

there's only one

Base Price

priceless, there's only one and it hasn't been found yet