Underworld

Underworld is a PVP battle based event first introduced as a beta event on September 17, 2014 at 12:00 AM (PST). Gameplay revolves around head-to-head battles between two players, with each player battling using three lines of five cards, for both attack and defense. Each respective line will battle against the other, with the player winning the most rounds winning the battle. Winning consecutive battles awards players reward bonuses.

Unlike regular battles, Attack power is not required to fight. Instead, Spirit Power (SP) is required. Each player is given a limited amount which regenerates over time. For this event, players are grouped in three different divisions based on the overall power range of player lines, for both attack and defense: Haunt of Souls, Sanctuary of Demons, and Path of Champions.

Rankings are determined by the amount of Underworld Points (UP) accrued by the end of the event, which are gained by winning battles and successfully defending against opposing attacks. Additionally, rewards are also handed out based on the amount of victories achieved in a player's respective division.