Battle Fury is a spell from the base set that grants 1 additional Physical Attack point to each of the active player's revealed heroes when they visit the dungeon. So if there are four heroes, the player would add +4 to their Total Attack Value in addition to any weapons and other effects.
Battle Fury's bonus is turned to Magic Attack by cards such as Goodberries and Arcance Energies for the respective heroes that meet these card's requirements.
Each point is applied to each individual hero, however, so if an effect would remove a hero before battle is resolved then the bonus is lost as well.