You gain a +3 bonus to attack and damage rolls made with this magic weapon. When attacking the target must succeed on a DC 18 Constitution saving throw or take 2d10 fire damage and sheds bright light in a 20-foot radius and dim light for an additional 20 feet for 1 minute. If you score a critical hit against an undead creature or kill an undead creature, it must succeed on a DC 15 Constitution saving throw or be slain instantly and be reduced to ash.
Proficiency with a Longsword 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.
Sap. If you hit a creature with this weapon, that creature has Disadvantage on its next attack roll before the start of your next turn.
Notes: a Paladin of good alignment and 15 lvl or above, Versatile, Sap