Unnatural Selection?

Unnatural Selection is the 17th chapter in Chrono Trigger. This is where Crono's party finally defeats Azala once and for all.

Happenings
Crono and his friends enter the Tyrano Lair only to be attacked by numerous prehistoric creatures. Fighting their way through the castle, they make it to the upper levels to find Azala, who unleashes the Black Tyrano on them. As the battle begins, a bright red star is seen in the sky.

When the battle ends and Azala and the Black Tyrano are beaten, Azala explains that the star will crash down to earth ushering in a long ice age. Ayla mentions that in her language, "La" means fire and "Vos" means big. They soon realize that Lavos is the entity that's crash-landing on earth. Lavos descends from space in the Prehistoric era.

Kino arrives with the Dactyls to rescue Crono's party just before Lavos crashes down on the Tyrano Lair.

When it hits and the dust settles, they return to the Lair to find nothing but a giant crater. Within that crater, is a newly formed Time Gate. Knowing that Lavos is deep underground where they can't reach it, Crono's party jumps through the Gate.