Seems to be able to have captured that dark and weird feeling of the battle I think. Smithy was one truly weird final boss since he went through different head forms too.
The drums maintain a very nice and simple beat that seems easy to follow and even play. The stringed instrument sounds great. Also I hear a xylophone. The bass sounds pretty pleasantly done on piano I think. The tune just has a dark demise feeling to it like this is your last chance to beat him once and for all.
Overall, excellent cover, excellent boss battle.