A couple of years back, in my own fantasy league, we started a playoff football pool. It was so much fun, we do it every year now, and have actually raised the main entry fee, so we can have some payouts leftover for the playoffs.
The rules are pretty basic, based on ppr (points per reception) fantasy scoring. You set your lineup using any players you want, but can only use a player once throughout the playoffs. The danger is, that you might have no QB options for the Superbowl if you use the 2 QBs early in the playoffs (it has happened).
It adds a bit of fun to watching the playoffs, and is a good way to extend the fantasy football season.
I made a league for the Detroit PSD forum folks, so if you want in, send me a private message with your email, and I will invite you.
It's free to get in. The winner wins bragging rights, and the losers feel the same as they do all year long watching the Lions....like losers.