Think I'm going down that easy?
The Midlight Reaper is vulnerable to Imperil, however, as it is already weak against the Fire and Ice elements, there is no need to inflict this status. Sazh should cast either Enfire or Enfrost on himself and Haste on both party members, and then switch to the Slash & Burn (COM/RAV) Paradigm for the main offense.
Despite the boss's fearsome appearance, it is not too difficult to defeat as it can be staggered quickly. It can also inflict Poison via its Nerve Gas move, so it is best if Vanille has learned Esuna as a Medic.
The Japanese name for this monster is Assault Cannon Löwe. Löwe is a German World War II-era prototype super-heavy tank.