If you visit Board Game Geek, they have pictures of many of the cards in the Trollfens expansion.
http://boardgamegeek.com/thread/1022569/got-mine-at-gencon-today
http://www.fantasyflightgames.com/edge_news.asp?eidn=4183
Harpy's have the Swarm ability, and their master has an action that allows you to move all minion monsters from his group, 2 spaces.
Throw in some kobalds and you have a big mess for the heroes. Couple with the fact minion harpys come with a green + blue dice, the ability to trigger swarm is like 80+% for them. We're talking some major hero beat-down.
I can't wait for Trollfens + new lieutenants.
-Cursain