This Seeking Tech guide will explain how you can beat Fulquilo in Metaphor.
This enemy is weak to the ice element, so make sure you have at least one Mage that can use Blizz. The other party members should focus on physical attacks.
When Fulquilo uses Hyper, move your party to the back row to avoid his upcoming Bonfire attack. Afterwards, you can move your party to the front row again to increase their attack power. The Mage can stay in the back since his magic power won’t be affected.
Continue this strategy until you defeat Fulquilo.