Unlock the throne-room rematch
Complete Chapter 1, talk to Shedletsky, then return to Blackrock Castle’s throne room. This 50 HP, Double Turns encounter is commonly called Cruel King DX. Winning unlocks Call: Blackrock King; it is not the same as the story Cruel King fight.
Mechanics references: Blackrock King · Call: Blackrock King
Last Stand: survive without letting him recover
Once, at lethal damage, he gains three turns of Persevere and +10 ATK for his next attack. A downed opponent heals him by 20 during this effect. He dies when it expires only if still at 1 HP.
Prepare recovery before pushing him into this state. If he heals through a down or a healing move, reduce him again; merely waiting three turns is not sufficient. The goal is to survive while preventing him from ending the window above 1 HP.
Choke and Famine need different timing
Choke grabs and lifts the target before twisting. It deals 8 and can steal 6 SP. Use a normal block: this move cannot be superguarded. Famine has a long fist wind-up; an unblocked hit deals 20, heals him by 10, and removes every copy of one selected item until the battle ends. Diversify recovery so that one deleted item family does not remove every option.
Do not use Ice Dagger as recovery
His Guardian passive sends Ice Dagger’s benefit to the boss’s team. Use another available heal. Scepter Strike also produces two mist impacts; guarding the first one does not finish the move.
Do not leave the final damage push to chance
Before bringing him to 1 HP, check which players can survive the next action and whether your recovery is still available after Famine. This is a survivability decision, not a reason to spend all remaining SP on an extra finisher.