Scilti Yscawntroet
One of five sons of Erim and one of the often neglected members of the party formed to help Culhwch locate Olwen.
Sgilti was chosen because he was so light-footed that he could march on the ends of the branches in the trees and weighed so little that even the grass did not bend under him.
Scilti might have a connection to a character named Cailte who is found in the Irish Fenian Cycle.
Source
Culhwch and Olwen | Late 11th century