S5·E32 Hisui Rises!

Princess Hisui and Arcadios are on their way to Fairy Tail when they fortuitously run into Natsu, Lucy, and Yukino. Princess Hisui has created something to send the wayward Celestial Spirits home by force, but the mother and son duo of Pisces appears to snatch it. And, like the other Celestial Spirits, this is a new, darker version of their previous selves. For example, the mother Pisces now has much bigger jaws...