Disclosure at Last? Xellos's True Form! - S2.E19

We find out that Xellos is actually part monster, and is extremely powerful. They (Xellos, Lina) manages to get away, only to have Saygram (the hencemen) follow them.

The others tries attacking but nothing works. Gaav shortly shows up, and when the gang think they are going to die... Martina shows up.

Martina uses her brooch looking thing as a shield (Lord Zoamelgustar!), and to everyone's surprise, it works. They manage to run away, and Auntie Aqua pops out of Martina's brooch.

Auntie Aqua then reveals the truth, saying she is what's left of the Water Dragon King from the many years ago. She tells them to head to Katahto Mountains where the original Claire Bible is being held. She breaks a doorway for them, and they all manage to escape.

Eating at an inn, Martina finds out that Xellos is part monster, breaking her heart. What surprised them the most, Gourry knew this all along (before the rest of them.)