Despite the commander, this deck does not aim to win by milling. Instead, Mirko is there to generate resources for the deck to use: He fills the enemy's graveyard, then knocks himself out with cards like Spelltwine, Rise of the Dark Realms, the black and blue primordials and others. This makes the deck highly adaptable and versatile. The way it wins often changes dramatically based on what the enemy is playing.
Since many of its creatures need to attack to get their effects off, there's a small set of cards to grant them haste or help them become more difficult to block. Could be that the deck should use even more of those, though.
Another small subtheme is playing cards from the enemy's hand and library, since there's a couple of cards there that fit well with what the deck already does. If you're already playing Ink-Eyes, Servant of Oni, for example, why not pack in Silent-Blade Oni as well?
Overall, the deck is already very fun and flexible, but it doesn't feel fully optimized yet. I'm thinking of getting rid of some of the more clunky cards like Grave Betrayal and Hedonist's Trove, even though they're fun. If you any ideas on how to improve the deck, I'd welcome them!
I love the concept of the deck. How about also adding cards for mass discard? That way you could also play cards from their hands when they're discarded to the graveyard as well? That should round out your game plan.
Interesting idea, thanks for your suggestion Discard could certainly give this deck a power boost. Though I've found that I usually don't lack for graveyard cards to play - Mirko does a really good job of filling them up, he often mills for a lot more than people expect. The reason he's the commander in the first place is so I only need to devote this one card to enabling the deck and can focus all the others on exploiting the graveyards. Still, discard has value beyond filling graves, so it might be a very synergistic way to power up the deck.
Wheels are an excellent idea! Disruption, grave-filling and draw, those could do some real work. For graveyard disruption I have Hedonist's Trove and Ghastly Conscription at the moment, though those are expensive of course. At least one cheap disruptor to tutor for in a pinch probably wouldnt' go amiss.
The problem with cards like Tormod's Crypt is that they're so limited in this format. At least the spellbomb draws a card. I always advocate for Relic of Progenitus and Bojuka Bog over things like crypt. Serving at least one other function is critical.
The mana cost of cards versus the number of lands you play and mana ramp, just doesn't match up at all. Its a very high end mana intensive deck and you simply do not have enough mana to fuel it.
I'd change the title of the thread to "Mirko Vosk - another man's graveyard is our man's treasure", just to match the well know saying "one man's trash is another man's treasure", and to play around with the idea of them and you. You can do this via the "Tools-->Edit Thread" option at the top of you OP.
An most interesting "theft" commander choice, perhaps playing on the hidden sub-theme of vampires? I will have to look into this idea and report back if anything worth while is uncovered... In the meantime might I recommend the inclusion of Raven's Crime, it is an repeatable way of disrupting your opponents while converting otherwise dead lands into something able to be exploited, especially with your particular game-plan. Another solid option if you enjoy raven's crime is Oona's Grace but with potential use of an surprise deck' win.