Continue exploring the dark world. This monster must first be “frozen” by stopping time, and then not allowing it to escape, defeating it. And yes, it’s better to do this without a hat on your head.
To do this you will need Celestian power. But be extremely careful - this power runs out very quickly. Usually you need to first use a time stop spell, and then empty the monster's health bar with other Celestian spells.
Before the battle, make a save and practice until you understand the principle.
