The Path was unlike anything Arthur had seen before because it looked like a tree of red road that sat behind the wilderness between it and Sith Town. As Whisker explained, this red light attracted monsters, so anyone who wanted to enter the Path would have to either slither through them or kill them.
The monsters outside the walls came in layers, as the ones on the periphery were the weakest: elemental slimes. These creatures were astral parasites, similar to the undead, but inhabited the condensed elements in nature.
Their existence was rare because elements needed to condense in almost a liquid form before they gained consciousness. However, certain minerals or monster cores have a high affinity to elements, allowing them to turn into slimes over time.
These slimes could then defend themselves by attracting elements at will and attacking whoever approached them. Due to their none biological nature, these parasites were not considered predators.