The Underworld of Secrets will be the second booster set for the Hero Cluster for Force of Will, and will extend the Moonchild card-type. It will be sold in 10-card booster packs, and will include a total of 150 card types with the following rarities: 61 Normal, 16 Rare, 5 Rare J-Ruler, 12 Super Rare, 1 Super Rare J-Ruler, 5 Marvel Rare, 12 Ruler with 4 Moonchild Ruler, 5 Secret, 8 Will Coin, 1 Token, and 24 Life Counter cards.
The packs will be available in 36-pack display boxes, with a PR promo card in each display. The new set will launch on November 25.