Unlike Claire's teleportation where she could just open a portal through space and appear anywhere, Arthur's version felt like a cheap knock off of the ability.
His version allowed him to split through two realities; the shadow world and the magic realm. The first portal took him to the shadowy world he usually trained from and the second portal let him out. Somehow, the distance between two points was greatly cut whenever he used the shadow world as a mode of transportation.
All he needed to do was visualize the place the second portal had to appear. It wasn't always perfect but was handy.
He walked out of the black tear in space before stumbling forward after tripping on a root. The black portal closed and its eerie aura disappeared with it, leaving him alone in the forest's heart.