Titled: Slapsgiving 2: Revenge of the Slapbet, things get crazy in this episode, where Marshall bequeths a slap to Ted and Robin, much to the chagrin of Barney. Meanwhile, Lily's long lost father (Chris Elliot from 'Everybody Loves Raymond') shows up.
This sounds like a good episode. The question will be what Marshall does with the last slap. I think there are 2 possibilities: 1: its in the last episode or 2: We see it in a 'flashforward'.