You gain a +3 bonus to attack rolls and damage rolls made with this magic weapon. In addition, the weapon ignores Resistance to Slashing damage.
When you use this weapon to attack a creature that has at least one head and roll a 20 on the d20 for the attack roll, you cut off one of the creature's heads. The creature dies if it can't survive without the lost head. A creature is immune to this effect if it has Immunity to Slashing damage, if it doesn't have or need a head, or if the DM decides that the creature is too big for its head to be cut off with this weapon. Such a creature instead takes an extra 30 Slashing damage from the hit. If the creature has Legendary Resistance, it can expend one daily use of that trait to avoid losing its head, taking the extra damage instead.
You have Disadvantage on attack rolls with a Heavy weapon if it's a Melee weapon and your Strength score isn't at least 13 or if it's a Ranged weapon and your Dexterity score isn't at least 13.
A Reach weapon adds 5 feet to your reach when you attack with it, as well as when determining your reach for Opportunity Attack with it.
A Two-Handed weapon requires two hands when you attack with it.
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.