Malefic Seal is the fourth map of the Alternate Netherworld bonus stage in Disgaea: Hour of Darkness.
Strategy[]
This map counts only 3 enemies. However, they can't be underestimated.
Dragons are monsters with a lot of HP, high attack power and a decent counter rate. To avoid unneccessary damage from the counters, use long range attacks or skills, or magic. Also, give your fighters the best armor (defense) you have and keep a healer nearby to recover lost HP.
It will take the dragons 2 turns before they are within attack range. So you can safely use the first turn to buff your characters with support magic: Shield and Braveheart for your melee fighters, Shield and Magic Boost for your casters.
Focus your attention on one enemy at the time to eliminate one of the dragons as quickly as possible.
If this map is giving you any trouble, it is recommended to either strenghten your equipment through the Item world or to level up your characters. A great place to do this is Cave of Ordeal 3.