Darkness is a great source of adrenaline.
(Self): Speed +3 (lvl 1) +5 (lvl 2) if alone in the room
Attack Power +12 (lvl 1) +18 (lvl 2) if alone in the room
Effective for a scouting hero or when one needs to quickly meet up with the team. Keep the hero away from the group to attract mobs then run back if the fight is too much.