Demon's Portal in Light World
Starting at level 99, you gain access to the Demon's Portal, a special dungeon.
The Demon's Portal can be entered once a day to fight against an extremely difficult enemy.
The enemy always regenerates its health by 10% at midnight.
Defeating the enemy is worth it because with each defeated opponent you get a permanent bonus of 1% to your hit points. As there are 50 enemies to defeat you can achieve a maximum bonus of 50% through the Demon Portal.