Scrag are creatures of Ancient Caldonia. They magical abilities including the ability to summon giants (Episode 38) and the capacity to phase in and out of trees (Episode 35). The tallest tree in the Haunted Woods was used by the Scrags to travel to & from Caldonia to an unknown destination. (Episode 38)
The Scrag were known to be hostile to the Human Civilization of Ancient Caldonia. In the night or dark, they would strike on human settlements. They were also known to eat the flesh of their human victims, as told in a series of Murals in the Temple to Bellum in Swampside (Episode 26).
The Scrags kidnapped and tortured people, as discovered when the Caldonian Expedition found a torture cave (Episode 30).
Humans fought against the Scrag. venturing into the forests to combat the Scrag, as the Scrag continued to assault townships of ancient Caldonia. Eventually the solution of killing the trees to stop the Scrags was enacted (Episode 26).
When Caldonia froze over 1500 years ago, the Scrags retreated into the mountains (Episode 38).
In modern Caldonia, most trees are dead, limiting the movement of the Scrag. However there are spots on the continent where there are living growing trees (Episode 17). Many trees were planted by a group of mysterious elves living atop of a floating island, who come once a year to plant trees (Episode 38).
A living scrag was first spotted in (Episode 37), they were a spellcaster able to summon monsters and cast offensive spells.
A living scrag wearing chainmail and using a sword was seen in (Episode 39).