Weapons that have the momentum property pack more of a punch the faster they move. When you make an attack, and land a hit, you may choose to deal no damage and build momentum for d3 turns. When building momentum your movement is halved. If you take damage or take any actions that are not an attack with the weapon you lose your momentum. If you succeed an attack you may expend your momentum. When you expend your momentum you deal weapon damage x momentum + 1d10 + modifiers.