What are the most dangerous unit combinations in Dungeon?

Excellent combination – Furies plus Riders – charge with the Riders to hit someone, and then attack the same unit with the Furies (the Lizard will add a bite). In this combination, the hero Sorgall will be good, as he will increase the defense and attack of the Riders (they are fragile and won't last long). Another good combination is Erin and Shadow Lords (Witch Coven ability), but I've noticed that the witches respond much more often to Lightning or Chain Lightning, and it doesn't work very well with a simple attack or other spell.