Kerberos

Kerberos: An artificial Undead born from the card Kingston made from the DNA of all 53 Undead, surpassing the Black Joker itself, Kerberos was created as the fifth Ace that Kingston intended to be the victor of the Battle Fight he set up. Unlike the previous creations, Kerberos was beyond Kingston's control, attacking his entire staff upon being born from the Stone of Sealing. The Undead succeeded in absorbing the decks of Heart Warrior & Club Warrior, along with Jack & Queen cards of Diamond Warrior. Kerberos even overpowered Spade Warrior King Form at first, but was defeated by Royal Straight Flush.

But Kingston sealed the Undead himself into the Change Kerberos card for his true plan: Using a surgically graft device based on the Rider System technology to fuse with his creation, becoming Kerberos II with Kingston's face on the monster's chest. It took all four Riders to fight Kingston/Keroberos II, with Spade Warrior King Form's Royal Straight Flush & Wild Heart Warrior's Wild Cyclone to negate the fusion. However, the Giraffa Undead takes the Change Keroberos for himself in the fight's aftermath for his own agenda.

Though thought to have been lost in the fight with Giraffa, the Change Keroberos was later used as the Ace card for Kamen Rider A-King, with two copies of the card used in creating Riders A-Jack & A-Queen.