My Geth, Lord of the Vault
deck has a Mill sub-theme in it, mainly to give Geth more targets for his ability. Wrexial, the Risen Deep
also works well with a milling sub-theme. However, I'm not sure how well mill works as a win condition. Oona is the only legend I know is more or less able to pull it off, because she exiles instead of just putting the cards into the graveyard. Szadek, Lord of Secrets
may also be playable as a mill commander.
Either way, if you are going to use a mill theme, look for cards like Mindcrank
(mills everyone but you, and triggers on damage, which everyone is doing anyways. Keening Stone
can finish off somebody who's been milled, and Grindclock
you can charge up to mill them for a lot. Leyline of the Void
keeps any "shuffle into your library" effects from occuring, as to Nihil Spellbomb
and Relic of Progentius
. Bitter Ordeal
can really hurt a player after you mill a bunch of cards, as can Sadistic Sacrament
. Finally, Memoricide
effects can deal with annoying "shuffle your library" eldrazi and such.