Slayers (1995) : 1x22

Lina and her friends rush to the lowest level of Rezo's institute. Tiva, the demon who has been guarding the institute gets in their way. Tiva is easily beaten by Lina as his magic was sealed by Rezo. Tiva guides our heroes to the lowest level and they break the last seal to enter the laboratory. The laboratory is filled with junk and as they look for Rezo's secret they have no clue what's what. Tiva pulls out a mask which allows him to unseal his magic power. Tiva then regains his power and attacks Lina and her friends. Tiva's evil magic is too powerful to destroy but our heroes manage to find a copy of the Claire Bible. All of Rezo's secrets are written in this book and they manage to crush Tiva.