Kerberos

Kerberos (ケルベロス, Keruberosu) is an enemy which appears in Suikoden.

Keberos are likely the most powerful enemy you'll encounter at the Floating Fortress of Shasarazade but if your party is at a relatively comparative level, they should pose little problem save for whittling down your HP in multiple battles. They are completely immune to fire magic and as such fire spells will always do 0 damage.

Etymology
Kerberos is the Greek name of Cerberus, the multi-headed hound (usually three-headed) which guards the gates of the Underworld in Greek and Roman mythology, to prevent those who have crossed the river Styx from ever escaping. It is the son of Echidna, who is the namesake of the monster Ekidonna.