Slayers - S1: Episode 23
Warning! Eris' Wrath!
We find out that Rezo is actually a copy and maybe Vrumugun is disguise. Eris uses the tablet to bring forth Zanaffar, a demon beast who destroyed anicent Sairaag, and could be a match for Shanbrango if they fought.
Lina tries to stop Eris completing the process. Eris manages to hit Gourry’s forehead with one of her jewels that controls him to attack (or kill rather) Lina. They fight for a while, and thanks to Sylphiel’s small knowledge of magic, Zelgadis tells her to cast a Flare Arrow. It’s small as a pen, and he aims it for Gourry’s forehead. He snaps out of it, and they watch above as Eris starts the process again. She hails Rezo’s avenge.
Just before Zanaffar is being (re)born, “”Rezo”” turns on Eris, and kills her with a shot thru her body. Eris falls, as “”Rezo”” agrees to her commitment on avenging Rezo’s death on his terms as he removes the jewel from his head and breaks it.