Think I'm going down that easy?Sazh
The Midlight Reaper is vulnerable to Imperil, however, as it is already weak against the Fire and Ice elements, Deprotect should be prioritized instead. Sazh should cast Haste on both party members, then either Enfire or Enfrost on himself in addition to Bravery, and switch to the Slash & Burn (COM/RAV) Paradigm for the main offense, utilizing Blitz for massive damage.
Despite the boss's fearsome appearance, it is not too difficult to defeat as it can be staggered quickly. It can inflict Poison via its Nerve Gas move, which can be cured with antidotes or if Vanille has learned Esuna as a Medic, though it isn't too concerning.
The Japanese name for this monster is Assault Cannon Löwe. Löwe is a German World War II-era prototype super-heavy tank.