Flail of the Flying Fist

Weapon (flail), very rare (requires attunement)

The head of this flail is the clenched fist of a retired iron golem, which is connected by a chain to the rest of its hollowed gauntlet. You gain a +2 bonus to attack and damage rolls made with this magic weapon.

When you make an attack with this weapon, you can use your bonus action as part of the attack to first reel in the chained fist to the top of the flail. When you then make the attack, the fist rockets from the top of the weapon, increasing your reach with the weapon by 10 feet for that attack and scoring a critical hit with it on a roll of 18–20 on the d20. If you score a critical hit against a Huge or smaller creature in this way, the target must also succeed on DC 16 Strength saving throw or be knocked prone.

Reel Big Punch. You can use an action to reel in and overcharge the rocketing fist. When you do, the reeled-in fist flies out from the weapon in a 30-foot line that's 5 feet wide. Each creature within the line must make a DC 16 Dexterity saving throw. A creature takes 5d8 bludgeoning damage on a failed save, or half as much damage on a successful one. A creature that fails the saving throw by 5 or more is also knocked prone. The fist and chain are then reeled back in to the weapon's normal length. This property can be used three times, and the weapon regains all expended uses of it daily at dawn.

Don't challenge an inventor to throw hands.