Whenever Mirko Vosk deals combat damage to a player, that player reveals cards from the top of their library until they reveal four land cards, then puts those cards into their graveyard.
Mirko Vosk is a dedicated mill commander: connect with his evasive flying body to dump big chunks of opponents' libraries, then back him up with a critical mass of mill spells and engines to grind everyone out simultaneously. Early turns develop ramp and protection, mid-game lands a few hits to soften players, and the late game closes via overwhelming mill plus 'punish empty library' payoffs.
Innate evasion (flying) makes his trigger reliably land
Mills variable, often huge chunks since it digs until four lands
Blue/black gives the best mill spells, card draw, and recursion in the format
Pressures all opponents toward decking out at once with the right support
Mill is one of the slowest win conditions and can fuel opponents' graveyard strategies
Highly creature-removal dependent; he's a 5-mana 2/2-class body that dies easily
Reanimator, dredge, and delve decks love being milled
Politically threatening—everyone sees mill and may target you first