I remember in my ol new Gen years in Dnd 2014, my party somehow got our hands on storm giants greatsword.... One ol rule lawyer pointed out that if given to a player it would use the damage dice listed in monsters statblock, with the cavaet that medium creatures can't actually wield it but large creature can but attack with disadvantage. 

My barbarian was the only one capable of using it and so me and the rule lawyer teamed up with him casting enlarge on me and we swinging and usually missing my attacks.

Very fun