This is a video of my level 8x party taking on Professor K in the 400ms Point DLC, Seeker of the Deep. At 108800 HP, this guy may seem like a pushover, but one bad choice, coupled with Professor K's resistance, defence and reflect will have your party sprawled on the floor in no time.
This punishing dungeon has no save points and you'll spend at least 30 minutes turn tailing your way back to get another shot at the little fella.
He may be harder than The Immortal One if you do not know what you're doing and get your party wiped out by Annihilation. Most people that beat him used the new DLC items like Accelerator (Reduce casting time 3) or Rose Quartz (Turn Cast).
These items are obtained from mini bosses you encounter in Random fights along the last 9 levels (16B to 24B). However, some people claim to never get these items (rare drop) even after 5 hours.
In this video, I will provide rough details on how to defeat Professor K in 3 Turns.
Level 80+ Immortals (At least 8000 HP)
The following skills:
HP Boosting skills
Level 8 White Magic
Level 8 Spirit Magic
Lucky 0 Magic Damage
Nullify all elements
Reduce Casting time 2
Mental Stability 2
Weapon Guard 2
Slot +5/Slot +10
Before the fight, get your Immortals' HP down to 1 to 1000. You can do this by fighting Hellish Kelolons (Black Kelolons in 24B). Note that this must be done by 24B as there are no more random encounters after 24B. Attack these Kelolons normally and they will perform counters, usually taking your characters to near death. Use Complete Defence to keep low health characters alive and Turn Tail when all Immortals have yellow Hp.
Health Sed to full health and put him in the front row (so he will tank the few Forceus that Professor K casts) and the Immortals in the back row.
Equip Sed with the Curse Crest, Holy Guard and Quad-Element Seal.
Once the battle starts, just keep casting Reversa and hope for the best. If you're unlucky, Professor K will cast Reflect on his 2nd turn, meaning that your party will suffer 4 reflected Reversas hitting for about 40000 each. This is where Persistence pays off, if you have 2 HP or 860 HP, a 40000 reflected Reversa will only whack your HP down to 1. I took a big risk by taking 3 of my Immortals with 1 HP into the battle.
In total, I have faced Professor K 6 times. In the 4 times I failed against him it was always because my party or the majority of the party got wiped out. Sure you can use divide and complete defense but that means that your party can last only so many turns. Because Professor K always has Regenerus and Annihilation at his disposal, you will never be able to cover the 20400 HP he heals while ressurecting your party members who fall to Annihilation. This is definitely not a fight you can win if you play defensively and stretch it out.