Arbalest

"Whoever reads this note I just want you to know, the Arena is alive. This weapon can only be used if the Arena sees you as a myth."

- Arbalest Note

The Arbalest is a Specialized Weapon Variant of an "exotic linear fusion rifle" that is appears exclusively in Boss Rush.

Its creator is unknown, however a note is found attached to the weapon that references that the Arena in Boss Rush is "alive" somehow, which leads to speculation that the Arena created it.

Weapon Perks
Compounding Force is Arbalest's primary weapon perk. The perk allows the weapon to fire powerful slugs that will penetrate Bosses and cause massive damage to them.
 * Compounding Force

This weapon perk does not require any form of an unlocking process as it comes unlocked once reaching Arena Rank "Mythic".

Disruption is Arbalest's secondary weapon perk. The perk synergies with the primary perk where slugs that impact Bosses with Compounding Force will create a shockwave that will stun any nearby Bosses, creating the Disruption effect.
 * Disruption

Unlike Compounding Force, players will need to kill six Bosses using Arbalest in order to unlock this weapon perk, however assists do not count.