Several Vilia appeared to Lancelot when he was trying to find shelter for himself and Merlin, who had been badly injured in a Dorocha attack. Taking the form of water bubbles floating in the air, they assured Lancelot that they meant no harm and began to heal Merlin with their magic. They also surrounded them in a sphere of light to ward off the Dorocha, and promised to stay with them and protect them throughout the night (The Darkest Hour).
As water spirits, the Vilia were able to appear as the different forms of their element. They took on the appearance of water bubbles, for example, while speaking with Lancelot. They were also shown to be skilled healers, and were able to cure Merlin after he was touched by the Dorocha.
Like many other spirits, the Vilia also appeared to possess some degree of omniscience. They were not only aware that Merlin and Lancelot were needed to heal the veil between the worlds, but also that Merlin had great power and a future that had been written since the dawn of time (The Darkest Hour).
- It is unknown if the Vilia have any connection to Freya.
The Vilia were likely based on Vilas, fairies in South Slavic folklore portrayed as beautiful women with long blonde hair.
There are three kinds of Vila in Slavic mythology: those that live on land and in forests, those that live in the water, and those that live in the air. They were usually quite friendly, but were known to take revenge on people who insulted them, disregarded their orders, or approached their circles uninvited.
Vilas were known to seek the love of handsome, strong men and assist them against their enemies. Similarly, the Vilia assisted Lancelot and Merlin (the noblest knight and most powerful warlock) against the Dorocha. The Vilia were also similar to Vilas in that they were skilled healers.