Alright you dorks here's some tips for this boss.
My borrowed units are a V5 Tololo and a V3 Springfield. Kluk/SF are V6, Vivi V2, Mechty V0, QJ/TLL V6, Kot V4.

Def up buff: Appears when he puts up his shield. Use any dispel (QJ, Mechty, Tololo, etc). Its shield will decrease damage taken by 30% but there isn't much you can do about it so just hit it until it breaks. Your damage still counts for points.

Debuff: Boss will apply a debuff with his frontal swipe that turns into a stacking crit damage buff for your team when cleansed (like Nemertea). You want to cleanse (either AoE or ST) every turn to maintain this buff. Buff has a 2 turn duration so you must cleanse at the same point every turn if you want to maintain it on most units (eg. QJ ult -> Cleanse -> everyone else, every turn). Units with bonus turns such as TLL and SF will tick down the buff every action, making it nearly impossible to keep stacked.
**When stability broken, boss will also start with an AoE attack that applies this debuff.
- How to abuse: Reactive cleanses such as Mechty's ult will instantly cleanse after the attack lands in the middle of the boss' turn, much like Nemertea. This means that you can technically max out all 10 stacks on turn 2 if desired, as the boss applies this debuff twice on the first turn if stability broken.

I didn't test this but I'm pretty sure that if you kill the boss on turn 6 you lose points from the third shield not being activated.

Springfield specific tips:
Use Colphne's common key so that her S2 can cleanse. **IMPORTANT
Intense Penetration has no effect on her bird.
At V2+, mostly for V6:
If you want to stack her buff for as long as possible, SKIP or BASIC on turn 2, otherwise on turn 4 when you Ult->S2 she will lose her stacks.
Example rotation:
T1: Ult->S2 TLL
T2: Nothing (use another unit to cleanse such as Mechty, Kot, Vivi V2, etc)
T3: S2 TLL
T4: Ult
T5: S2 TLL->S2 SF
T6: S2 SF
T7: Ult->S2 TLL (Buff will fall off here)