Razorpine

Hold the button and it throws a tight spray of needles straight ahead, quickly enough that the stream reads as continuous rather than as separate shots. Each needle stops dead on the first thing it touches, enemy or wall, and starts falling once it has traveled a way out. That makes it a close to medium range weapon that wants a clear firing line. Fight it in a tunnel and most of the output disappears into the ceiling.

One target at a time. Sustained damage on a single enemy is high enough to keep pace with magic weapons from much further into the game, but with nothing homing and nothing piercing you have to aim it yourself and a crowd will bleed off half the shots. Planting yourself in front of a Frost Moon boss and holding the stream on it is exactly the situation it was built for.

It drops from the Everscream, and the odds climb with the wave, so a run that stalls out early will not produce one. This is a weapon you farm with a group or a properly built arena, not something you pick up on a first attempt at the event.