The Gwyllgi(ケルベロス) (Cerberus in the Japanese version) is a savage, three-headed hellhound. Its fangs are cruel death dealers -- Let alone the three gnashing jaws hosting them. The Gwyllgi is a promoted Mauthe Doog. This swift beast is possessed of great Strength, Skill and Speed, effectively making it the monster counterpart to the Swordmaster; this results in a highly dangerous, highly mobile beast. They have a low Resistance rating, making spells hit often and hard on them. Regardless of the unit it attacks, usually Swordmasters are the only units that will be able to double them, unless a Brave weapon is used.
- "Gwyllgi" literally means "Wild Dog" in Welsh. Its Japanese name, Cerberus, comes from the creature from Greek and Roman mythology.
- They appear on Floor 4 (as a boss) and Floor 7 of the Tower of Valni, and Floors 1-5 and possibly 7 and 8 of Lagdou Ruins.