A Dungeon Break occurs when a party cannot complete a dungeon and does not leave the dungeon. Monsters will continue to spawn within the dungeon, making it more challenging to clear. Once the dungeon cannot contain the monsters within, the boss will lead the beasts out of the dungeon and invade Terrasus.
Dungeon Breaks became quite a lucrative endeavor in Marcus' past life. Guilds would intentionally cause breaks within their territories. Once the monsters exited the dungeon, numerous effects begin to take effect.
First, their stats are increased two-fold. This makes the monsters far more formidable; however, only a certain number of monsters are allowed to exit at a time. If the monsters are defeated, more are eligible to leave; if they are allowed to rampage for a given time, more can exit the dungeon until every monster is released or defeated.