You gain a +1 bonus to attack and damage rolls made with this magic weapon.
When you hit a giant with it, the giant takes an extra 2d6 damage of the weapon's type and must succeed on a DC 15 Strength saving throw or fall prone. For the purpose of this weapon, "giant" refers to any creature with the giant type, including ettins and trolls.
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: Additional, Prone, Damage, Combat, Heavy, Two-Handed, Graze
Nice
Does anyone know the value/cost of this weapon?
Some 3rd party resources I've read indicate a value of 3000, 4600, or 7000 GP. So take those values with a grain of salt and adjust as fits your campaign, also considering that people selling magical items may price or sell their items higher or lower depending on their bargaining skills or their own knowledge of the value of such an item.