Before attacking Baron Gustav, the dungeon on Floor 1 was filled with beginner level hunters. After Isaac returned, their number was three times more than before. As a result, many monsters on Floor 1 were killed. It forced him to keep buying more monsters. Even though the monster birth rate was high, it took time for the baby monsters to grow and be ready to fight.
The zenny cycle between income and expenditure moved quickly. Isaac didn't get any loss, but he still wanted to optimize his income.
The trick was by building an exp grinding area.
Isaac ordered his monster to build a monument at some point. The monument had special effects within a radius of 500 meters. Every human who killed a monster in that area would receive an additional bonus experience.
If normally they needed to kill 100 monsters to get to level 2, then they just needed to kill 50 monsters in the exp grinding area. Humans could level up faster without having to kill a lot of monsters.
