While I had a relatively easy time likely due to my party's relative power, it's mostly about dealing with Raspatil's attack cycle being faster than yours. Raspatil has two gotchas:
You need to kill all the adds summoned before Raspatil casts Beseech. It will happen after a (somewhat extended) period time after every summon, so you can't stop focusing on adds until the end of the encounter.
You need to manage wounds to prevent yourself from getting into situations where your your party's max HP havehas been capped in the yellow zone, providing an opportunity for Raspatil to one shot you even with a dedicated healer.
- Lightning (RAV): level 13, no infusions
- Green Chocobo (MED): level 99, infused with Feral Speed II and Role Resonance (not used)
- Third slot wasn't used, wouldbut I'd suggest a sentinel for Combat Clinic (MED/MED/SEN) if needed
- Relentless Assault (RAV/COM/RAV) — Default
- Relentless Assault (RAV/COM/RAV)
- Diversity (RAV/COM/MED)
- Aggression (COM/COM/RAV)
- Fifth and sixth slots not used, wouldbut I'd suggest Combat Clinic (MED/MED/SEN) or Discretion (COM/MED/MED) if you can't heal fast enough in Diversity
- Paradigm juggle1 Relentless Assault (RAV/COM/RAV) to stagger Raspatil
- Use Lightning's Army of One feral link ability to pumpincrease the stagger chain up to 750-800%2
- PumpIncrease the stagger chain up to 900% in Relentless Assault
- Switch to Aggression (COM/COM/RAV) until adds wereare summoned
- Only switch to the adds a few seconds after summoned to maximize time on Raspatil
- Kill adds before Beseech
- Switch to Diversity to bringheal myself back up to the green zone3
- Go to step 1.
Unfortunately, Raspatil's attack cycle is a bit faster than mine, somine; adds get summoned earlier and earlier in the stagger period, and you start to get too low in health. So after the second or third stagger, I started switching to Diversity and targeting the adds immediately after they were summoned. This provided less time for damaging Raspatil, but kept the situation from spiraling out of control.
After the 5th or 6th stagger, Raspatil essentially lapped my cycle causingand caused me to miss a stagger almost entirely. This was a blessing in disguise, as it essentially resynced our attack cycles.
Once Raspatil was down to 25%, I used Serah and Noel's ultimates when the chain gauge was up to 850-900%. I also started to get a little more aggressive as well, staying in Aggression longer. Raspatil died while all the adds were active, so I just finished them off and completed the encounter.
Note 3: If my party's average max HP was 75% of what it should be due to wounds, I took one actionturn during this period to pop a Wound Potion to allow my Green Chocobo to heal me back into the green areazone.