Primeval

Primeval is the 21st episode of season 4 of the television show Buffy the Vampire Slayer.

Synopsis
Buffy and the original Scoobies finally manage to find out that Adam is hiding at one of the Initiative secret labs. Buffy, Xander, Giles, and Willow find a way into the depths of the Initiative and stop at a room near area 314, where Adam and his people hide planning to build and release an army of hybrid cyborg monsters. Buffy leaves through a secret door while the rest prepare a spell the significance of which is still not clear. Buffy finds Riley and leaves him fighting Forrest, now turned into a killer cyborg. Then she goes on to tackle Adam. Things don't look good for her at first, but then the significance of the spell is made clear: Giles, Willow and Xander invoke the powers of the primeval slayer and beg to be lead with her into Buffy's body so they can defeat Adam together. It works, turning Buffy into an eerie version of herself with the powers of the primeval Slayer and the help of the gang. After an intense fight in which she's able to use powers like stopping bullets in mid-air and turning them into doves, she manages to tear the uranium nucleus out of Adam's chest and kill him. After this, she falls down in the arms of a surprised Riley that arrives just in time to hold her.