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 damage them heavily. Due to their speed capable of reaching 28 with an average above 24 very few units have the capacity to double-attack 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.