Even with a cultivation of a million years, it was still just a sea beast.

Sea beasts may live long, but that doesn't mean they are all immensely powerful. Even the Dragon General under Emperor Wuji's command has barely reached the level of a Three Tribulations Supreme Emperor. The Death Sea Witch before them, despite its million-year existence, only possessed the power of a Two Tribulations Supreme Emperor.

However...

When three Semi-God Realm experts strike simultaneously, the outcome is predictable.