A Path
While Theo fought with his grandfather, there was also another grandfather fighting against multiple King Class Monsters.
He was none other than Leonardo, the War Saint. As expected, even though Theo seemed to have predicted everything. The number of the World Class Monsters surpassed Theo's original expectations.
If not for the fact that the Magma Dragon was coming to help, they wouldn't have enough people to take care of the enemy's World Class Monsters.
That was why they were in the current predicament. Theo simply didn't have enough time to kill more King Class Monsters.
In other words, the slime managed to counter Theo's plan with his overwhelming number.
Still, the slime might be able to win the first battle, but it was still within Theo's imagination. If the magma dragon didn't come, he could easily ask someone to handle two World Class Monsters. There were a few people qualified to do that like the Goddess of Death or even Theo himself.