Weapon (greatsword), rare
When you roll a 20 on your attack roll with this magic weapon, the target takes an extra 7 damage of the weapon’s type.
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: Damage: Additional, Damage, Combat, Heavy, Two-Handed, Graze
how would this work with Champion Fighters?
AEG33, I am perhaps 2 years late to answer this. But Champion fighters still critical at their reduced numbers, but the weapon ONLY checks for a 20 roll.