Like I said, it tore through the Witching Cloak.
Up until the arrow ripped it, the thing was indestructible to all attempts to damage it, including a dragon trying to burn it with fire and rip it apart after Blue wrapped it around his snout (Which resulted in the dragon actually exploding from the buildup of flame).
And the post war story has a major magic being released from a giant chest acting as a prison/siphon for it's power. I've only just begun that arc, but this being (Who kind of looks like a cross between Nightmare and Dream of the Endless) was able to disrupt all magic, on multiple worlds.. The magic simply ceased to work. And part of this beings power was bundled up in the Witching Cloak.