Patriarch's Seal

Patriarch's Seal is the first map of the Baal Castle bonus stage in Disgaea: Hour of Darkness.

Strategy
Both the Efreet and Surt are of the Great Wyrm monster class. These monsters have high HP and attack stats.

The Great Wyrm has access to high damage dealing area of effect attacks. So avoid grouping your characters together. Also, the Efreet has attacks with the fire element. So using characters with fire resistance will give you a slight advantage.

Try to take out one or two Efreets as soon as possible. The Surt might have a higher level, but he's not more of a threat than the 3 Efreets. Reducing their numbers quickly will prevent them from being able to gang up on a single character, mostly likely outright killing the poor victim.