You have a +2 bonus to attack and damage rolls made with this magic weapon.
Everytime you land a critical hit using this weapon, you must choose to either forgo the additional crit damage and store the energy for future use, OR release all of the previously stored energy in the form of +2d6 per crit saved.
Another benefit of storing energy is that the threshold for landing a critical hit is lowered by 1 each time you choose to store the energy from the crit. (ie. Forgoing a Nat 20 crit means a Nat 19 and up is a crit next time, then Nat 18 and up the time following that, etc.).
If enough energy is stored to crit on a Nat 1, then on a hit the player must release all of the stored energy (40d6) into that attack. If the player attempts to store the energy from a Nat 1 crit, the sword will overload and explode, causing 40d6 force damage to everything within a 30ft radius, including the wielder of the weapon. In this scenario, the weapon will be permanently destroyed.
After choosing to release the stored energy on a critical hit, the weapon resets to having no stored energy, and crits on a Nat 20. As long as the weapon is never destroyed, it retains its ability to store energy from critical hits.
Proficiency with a Greatsword allows you to add your proficiency bonus to the attack roll for any attack you make with it.
This weapon has the following mastery property. To use this property, you must have a feature that lets you use it.
Graze. If your attack roll with this weapon misses a creature, you can deal damage to that creature equal to the ability modifier you used to make the attack roll. This damage is the same type dealt by the weapon, and the damage can be increased only by increasing the ability modifier.
Notes: Bonus: Magic, Damage, Combat, Heavy, Two-Handed, Graze