I'm thinking, black otter colored mix breed.
Ears are way way too long for anything close to a netherland dwarf.
Silver martins are chinchilla based, and that one is agouti based, you can tell because of the brown fur behind the neck and tan colored belly trim.
He's missing the rufus or wideband to be an actual tan, and I think, even a 1/2 tan should have more rufus expressed than that guy has. :shrug:
Maybe a lop cross ?