Macemallow

Weapon (any melee weapon which deals bludgeoning damage), uncommon (requires attunement)
  With a shaft of marshmallow root and a light and fluffy ‘mallow on its tip, this sticky weapon is the toast of the puft blacksmiths’ creations.
  You have a +1 bonus to attack and damage rolls made with this magic weapon. When you roll a 20 on an attack roll, the target is covered in sticky marshmallow and is restrained if it is Large or smaller. A creature restrained in this way can use its action to make a DC 13 Strength check, freeing itself on a success.
  When you speak the command word (“smores”) while holding the weapon, the marshmallow bursts aflame, shedding bright light for 20 feet, and dim light for an additional 20 feet. The flames last until you speak the command word again or until you drop or stow the weapon.
  Rare variant: While aflame, the macemallow deals an additional 1d4 fire damage on a hit. Increase the DC of the Strength check to 15.
  Very rare variant: While aflame, the macemallow deals an additional 1d6 fire damage on a hit. Increase the DC of the Strength check to 16.