Season 9: Episode 13 - Slapsgiving #3: Slappointment in Slapmarra"

Slapsgiving #3: Slappointment in Slapmarra": As Marshall delivers the penultimate slap to Barney, Ted recounts how Marshall explained to Barney in advance the process through which he went in order to master the Slap of A Million Exploding Suns. He had to learn Speed, Strength, and Accuracy.