Despite their apparent invulnerability, Leviathans can be permanently killed, even in Purgatory, though how this permanent death comes about is unknown.

What are the Leviathans weakness?

Leviathan is weak to electricity but resistant to ice and fire attacks. To take down Leviathan, stay away from non-electricity magic and elemental summons. The boss is also immune to most effects. Be careful not to spam lightning too hard, or you'll run out of MP in a fight where Cure is effectively required.

Are Leviathans more powerful than angels?

Powers and abilities. Like some of God's earliest creations, Leviathans are very powerful beasts, more powerful than most other creatures and capable of killing and / or eating just about anything else. ... Even angels are powerless against the Leviathans.