Secrets of eternity was released in January 2015.
This set introduced the Infernoids. A series of monsters that can special summon themselves to the field by banishing other Infernoids from either the hand or graveyard.
Notable cards in the set include: Farfa, Malebranche of the Burning Abyss, Qliphort Monolith, Uni-Zombie, Nephe Shaddoll Fusion, and a card that would bolster Satellarknights to combat the Burning Abyss-Shaddoll meta: Stellarknight Constellar Diamond.
In this series, both Nyhmnim and myself will be opening 24 booster packs (or one box) of a core Yu-Gi-Oh! booster set. We will build a deck and play a best two out of three, and the winner will receive a small prize to upgrade their deck. However, in each episode we'll open another box of the next that was released moving in chronological order. Constantly upgrading our decks before dueling each other at the end of each episode.
This is the Yu-Gi-Oh! Progression Series.