Hahaha, very funny. Yes, you can do crossover art, but it has to take traits from BOTH inspiration sources, which you DID NOT DO. There's not a single trait in your drawing that says 'Grum' about it.
And also, as other people pointed it out on twitter, you included other Dark Soul characters in that fanart not just Yhorm.
You know, you really got on my nerves now, so I am gonna make sure people see this bullshit more.