If you've never seen WILTY, basically, one of the panelists tells a story and the opposing team has to decide if it is true or is a lie. The entire episode is in the video, but for the Mitchell possession bit, which is only 3 to 4 minutes long, start at the 20-minute mark.
The Sherlock Series 3 Mini Teaser episode has also been posted. Hooray for Sherlock! This one really is just the Sherlock makers teasing us via playing with the non-eponymous characters of the show.