The primary thing Guzzlord has to set itself apart from other dark types in the format is its dragon typing. Key resistances to water and electric allow it to wall Kyogre and Regieleki, both of which are very powerful offensive threats in the metagame at the moment. The resistance to fire is also great as it is able to switch into things like Entei and heat crash from Groudon. It also has access to wide guard as I stated before meaning it can completely nullify damage from things like astral barrage and water spout regardless of how much HP it or its teammate has remaining. The last thing is its ability to function as a win con with iron defense and amnesia, as it walls very common late game cleaner mons like Regieleki and Rillaboom.as much as I am a fan of Shiny Guzzlord I feel like it's just dead weight on the team when you could have better dark types such as goltres. It has almost 0% of usage in the current meta. On second thought it would pair amazingly well with Zacian imo. I have seen goltres with zacian-c alot recently and it's actually a thing with the help of snarl, sucker punch, foul play and air slash. I feel like guzzlord is a cheaper version of goltres and yveltal and would work well in Trick room.
I think it has more than enough things to seperate itself from goltres and yvel.