Instanced Mission : Arsene Secret Vault

Mission Information
Participation : 2 families (squad up with Cruz)
Character Lineup : Romina - STW - Grandice (mine), Grandice - Scout - Hellena (Cruz)
Requirements : 500 reputation points
Rewards : Magical Amethyst, Liquefied Gas, Piece of Trump Card, Medal of Honour, Buckle, Trump Armor recipe (rare), ELN recipe (very rare)
Frequency : daily
Duration : 30 minutes time limit. Average time of 12 minutes to complete mission.
Difficulty : Moderate

The Arsene Secret Vault mission has been available for quite some time now. The complete guide is detailed in BookOfWind. Being able to use three characters allows us to make full use of Enhanced Tactics Buffs, which make the mission a lot easier. I (usually) play the role of boss attacker whilst Cruz plays (with) Hellena. Loot rules are set to acquire by turn to equally split all loots, including Medal of Honor cards.

As the mission starts, we buff up (Principal + TA buffs + meditation) and pay the 500 reputation points to enter the 2nd room. I activate Bless and cast Refresh Mind my Romina before entering the 2nd room.Cruz runs around the area to avoid the mobs, but I assume his master Hellena will have no problem taking a few hits every now and then with the current armor she is equipped with (no need and useless to kill the mobs due to infinite spawn). In the meantime, I rush in to the boss to room do deal with to deal with Celine and an additional boss. As soon as my first Bless wears off, I activate it again (no need to wait for cooldown due to Refresh Mind) I want to keep my +1AR up and its additional benefits to finish the mission as quickly as possible. This procedure goes on as Prost, Emily and Mario are defeated.

Hellena's Armor : sturdy

 Once Mario is defeated, the cooldown for bless should be almost finished. Same buff sequence as the first room is done, including bless + refresh mind. The critical and hardest part of the raid is the last room. Upon reaching the last room, I rush to Celine to deal enough damage to her until Prost is summoned. I then focus on finishing Prost as soon as i can. This is because once Prost is dealt with, the mobs will disappear and Cruz can relax. Emily and Mario do not pose much of a threat. After dealing with Mario for the 2nd time, all that's left to do is kill Celine. During this time she likes to use attacks that inflict Armor Crasher, so Hellena is best kept away to a safe location. Defeating Celine will yield more loots, and the chance of Trump Armor Recipe and even Elite Le Noir Recipe.

Reduce Celine HP to make Frost appear - and kill frost ASAP!

Be careful of Armor Crasher