This spell is similar to the invisibility spell, but the recipient is able to attack, either by missile discharge, melee combat, or spellcasting, and remain unseen.
Note, however, that there are sometimes telltale traces, a shimmering, so that an observant opponent can attack the invisible spell recipient. These traces are only noticeable when specifically looked for (after the invisible character has made his presence known).
Attacks against the invisible character suffer -4 penalties to the attack rolls, and the invisible character's saving throws are made with a +4 bonus.
High Hit Dice creatures that might notice invisible opponents will notice a creature under this spell as if they had 2 fewer Hit Dice (they roll saving throws vs. spell; success indicates they spot the character).