Greatbow

The bow must anchored into the ground to fire and takes a bonus action to do. The user cannot move after firing this bow.

For making the attack roll use DEX mod, but use STR mod for the damage.

Ammunition (range 200/800), heavy, special, two-handed. 

This bow's substantial size(6 ft tall) necessitates the use of specialized great arrows and a size of large, or the powerful build to wield.

The Greatbow deals 2d6 piercing. 

The bow weighs 20 lbs

Special. When using this weapon to attack a target within 20 feet, you have disadvantage on the attack roll.

Did you know that a regular longbow is actually about 6 feet tall?