The character brings into being a shimmering, swordlike plane of force. The sword strikes at any opponent within its range, as the character desires, starting the round that the character cast the spell. The sword attacks its designated target once each round. Its attack bonus is the character's level + the character's Intelligence bonus or the character's Charisma bonus (for wizards and sorcerers, respectively) with a +3 enhancement bonus. As a force effect, it can strike ethereal and incorporeal creatures. It deals 4d6+3 points of damage, with a threat range of 19–20 and a crit of x2.

The sword always strikes from the character's direction. It does not get a flanking bonus or help a combatant get one. If the sword goes beyond the spell range from the character, if it goes out of the character's sight, or if the character is not directing it, the sword returns to the character and hovers.

Each round after the first, the character can use a standard action to switch the sword to a new target. If the character does not, the sword continues to attack the previous round’s target. The sword cannot be attacked or harmed by physical attacks, but dispel magic, disintegrate, a sphere of annihilation, or a rod of cancellation affects it. The sword’s AC against touch attacks is 13.

If an attacked creature has SR, the resistance is checked the first time Mordenkainen’s sword strikes it. If the sword is successfully resisted, the spell is dispelled. If not, the sword has its normal full effect on that creature for the duration of the spell.