“Ferocious, three-headed hellhounds. Their triple-fanged bites are difficult to dodge.
—In-game description in The Sacred Stones
The Gwyllgi (ケルベロス Keruberosu, lit. Cerberus in the Japanese version) is an enemy-only Monster class that is exclusive to Fire Emblem: The Sacred Stones. The promoted form of the Mauthe Doog class, these savage, three-headed hellhounds are significantly more dangerous than their unpromoted counterparts, ripping the flesh of their foes with deadly attacks administered by their fangs. Gwyllgi are distinguishable by their three-headed forms, alongside a mane that is murky green in colour.
Gwyllgi often possess high Skill and Speed, as well as decent Strength, making them particularly suited to killing slower, weaker units. Their maximum stats are equal to those of a male Swordmaster, but their bases and growths are superior. Furthermore, they have a Movement range that is equal to that of a Paladin. Players should pay attention to the weapon they have equipped; Hellfangs are functionally equivalent to Silver Swords, while Fiery Fangs are functionally equivalent to Iron Swords. Gwyllgi equipped with Hellfangs are clearly more dangerous, and extra caution should therefore be exercised when facing them in battle.
Due to their high Speed, typically surpassing even that of a Swordmaster, very few units will be able to beat them in this department. It is not uncommon for Gwyllgi to have Speed as high as 24, and some even go up as high as 28. While their defenses are very poor, they are typically just enough to avoid getting killed in single blows by anything short of a legendary weapon. Because of this, units with high enough Defense to shrug off Gwyllgi attacks are recommended to be deployed when faced with such creatures on the battlefield..
Gwyllgi can be encountered as enemies on Floors 4 and 7 of the Tower of Valni, alongside Floors 1-5 and possibly 7 and 8 of the Lagdou Ruins.