FGO Ordeal Call Challenge quest Merman Sea battle 3T with NP4 Rama

From multiple attempts, learned that the gimmick seems to be that the enemies can only be given significant damage when the enemy with the special buff is defeated in tghe rightmost column,
Then that the merman is demonic, so finally had an excuse to skill Rama, who has spooked me in multiple gacha rolls.

#fgo