This whole scene is So good it kills me...
Just like in their first fight, Ras descends from the skies to get something he needs, and knocks the shit out of Riyu, and knocks Arin around, but this time instead of delivering his monlogue to Riyu, it's to Arin, and it isn't menacing as much as an "I know your potential," type of thing...
He doesn't see anymore potential in Riyu, but Arin, he sees Arin, he knows Arin, because at one point, he WAS Arin, a weak, pathetic, puny child... Arin's Spinjitsu is still just as shit as when he first faced Ras, and he's still just as weak, which Ras tells him. He tells Arin as much, how he's still as weak as their first encounter, and how once, he was weak like Arin, that the ninja are squandering his potential and holding him back, and Ras tells him how he found his master, who taught him the most essential power, strength.
And then there's that moment at the end where he gives Arin this look of just "I know you, I've been you, maybe one day you can find someone to teach you as I was taught..." and then the end where he hallucinates his parents running towards him...
This scene, along with the finale and Lloyd's episode 1 vision, really feel like they're setting up a darker path for Arin and I'm So excited for that possibility...