Font of Power
Due to planar energy, the presence of a powerful artifact, or some other factor, this terrain boosts certain kinds of attacks.
Effect: Choose one power keyword, such as fire, evocation, or arcane, for a font of power square. Attacks that have that keyword made in that square gain a +5 bonus to damage per tier.
Usage: A font of power is a good way to make an average encounter into a hard encounter, and a hard encounter into a deadly one. Have the font squares fill most of an encounter area and use an elite or solo creature with one or more attacks that are keyed to the font of power’s damage bonus to increase its damage output and get the characters’ attention.
Published in Dungeon Master's Guide, page(s) 68.