Hyperdense Melee Weapon Template (5e Equipment)
From D&D Wiki
Amount of damage dice is multiplied by 5. Weight is multiplied by 1000. Weapon gets Hyperdense property.
Hyperdense: Hyperdense weapons are so unfathomably heavy that they need a built-in antigravity device just so it's practically possible to lift them off the ground, let alone wield them with any effectiveness. The antigrav runs for 24 hours on one energy cell, and while it's on only (weight of non-hyperdense weapon counterpart) lb. of the weapon's weight counts towards your encumbrance. However, it still strikes with the force of its full weight.